These tips are for clothes that the wearer can't take off while going about their normal life, so the clothes have to look mostly normal. Since we all (or almost all ;-) ) wear clothes everyday, and are used to not taking them off during the day, there has to be some incentive so that the wearer would want to take them off, but can't. There are several reasons to make wearing specific clothes less attractive:

(Un)desirable features of clothes

1. Limit mobility. Most obviously a hobble skirt or longer pencil skirt that limit your step, but clothes where the arms and/or legs are tight and not stretchy will limit how far the wearer can bend arms, knees, hips, or reach up. 'Cold shoulder' jumpsuits with straps hanging over the upper arms might also limit arm reach. Locked on gloves, like opera gloves, are limiting too: the wearers agility and feeling are less in their hands, you can't wash your hands or let them get dirty (you might wear rubber gloves over them for that), and you can't operate many touch screens. Locked on or attached mittens limit even more. Niqabs, veils, wide-brimmed hats might limit vision, and enveloping clothes like burqa or long rain coat with only slits for the hands can hamper you in several ways.
   You can also add to the limitations by for instance sewing closed the split of a skirt, sewing the upper arms to the sides, or sewing the legs of a split skirt (also skort, culotte) together.
2. Discomfort. Clothes that are a bit too tight, rough, have irritating seams, or exert constant pressure (even a little can get annoying after a while). Examples can be regular clothes but a size too small, locking footwear with high heels, corset/corselet/support panties etc.
3. Embarrassment. Wearing clothes that are less appropriate to the situation, or clothes that you would not normally pick, like childish, tacky / very sexy, out-of-fashion, rainwear when it is dry. Examples are a onesie outside, serving guests in a maid costume, deep cleavage, very short skirt, etc.
4. Bathroom Access. Any locked-on pants, overalls, jumpsuit, hobble skirt or skirt/dress with attached panties won't allow bathroom visits. A challenge could be to hold for as long as the wearer can, force them to wet themselves, be required to (publicly) ask permission to go, or need to wear a diaper and use it. (In the last case the keyholder can be absent for a longer time.)
5. Access to your own body. Of course you can't beat a chastity set for denying you access to your sensitive parts, but with one-piece suits a large part of your skin is inaccessible, and zentai suits cover 100%. That means no washing, it's harder to scratch, ...
6. You can't take off what you wear underneath. For example diapers, dildo's and plugs, things like thongs or bodies that creep up in the butt crack, embarrassing t-shirts under overalls, rough or scratchy underwear, ...
7. Annoyance. Things that rattle or tinkle like zipper pulls, ribbons or tassels that hang in the way or tickle, straps slipping off the shoulder or closures that spring open. (Of course the latter annoyances are a bit contrary to the wearer not being able to remove them.)

Things to look for to prevent taking clothes off

In general clothes that cover more of the body offer more opportunities to limit the wearer; I've mentioned many options above. On my securing in clothes page there are many tips on how to prevent someone from taking specific clothes off, but in general snaps (UK: poppers), Velcro and hidden zippers offer no easy ways to lock, though usually you can add some D-rings on either side of the closure that you can padlock closed, or replace them with better types. And of course clothes that need no closure because they are stretchy (contain elastane or spandex) or are elasticized are hard to lock too.
A note on zippers: for the common 5mm plastic coil zipper you can get locking sliders, and most larger zippers have one a hole in the zipper pull that you can put a padlock though, but the small zippers with the fiddly pull don't offer much to attach to.

Overalls

With overalls it is easiest if the bib and back are high enough that the wearer can't pull the straps off the shoulders, and it the waist is close fitting enough that they can't be pulled down without opening the closures. (Otherwise you could use a belt.) Belt and hammer loops on any type of clothing make nice attachment points. If you want hidden bondage, straps that button on the inside of the bib can be locked without the padlock showing at all.

Jumpsuits

If you can't find a suitable jumpsuit where e.g. both bottom and top are tight enough to limit mobility, you could also combine pants and a top or jacket into a one-piece suit: you can sew them together (for instance at the back, the sides and on both sides of the front closure), or put D-rings along the bottom of the jacket that you can padlock to the belt loops of the pants, or weave a chain through. (D-rings on the inside would keep the bondage hidden.) If the top needs to be taken off over the head, locking top en bottom together is already enough to prevent them from being taken off. You can do the same with a top plus tight skirt.

Closed at the back

Clothes don't always need to be locked on to prevent taking them off: many people can't undo a back zip and even more require help with back buttons, so a dress or jumpsuit that closes in the back might already have the same effect as locking. Wearing a onesie or overalls back-to-front might already be enough. Front closing jumpsuits that are close-fitting can be very hard to get your shoulders out of.
There are even overalls where the straps attach at the back, especially overalls from the 1940's regularly have that, like Simplicity pattern 8447. Some of those overalls also button at the back. When the straps button high enough on the back, and especially if the straps cross, the wearer will be stuck in them. 1930s beach pajamas can be of similar construction. (You can see a cute example in the episode 'Peril at End House' (1990) from Agatha Christie's Poirot series.)

footwear

Footwear with high heels is also something the wearer at a certain point will want to take off.

Shoes/sandals are a bit hard to make locking. There are straps to lock any pair on your feet, like this, but you can't really hide those. You might be able to attach loops to the top of the back of a normal pair, like this, and put your own ankle cuffs though them, but I'm not sure how easy that is and how strong you could make it. Some shoes and ankle boots already have such loops though, so they would be useful. Otherwise you might be best off just buying a locking pair. Buying a pair with a cuff through such a loop as in the previous link, you could probably also wear them without the cuff and they should not draw too much attention.

Boots with a zipper should be easy to make locking, by replacing the slider - as long as they have a 5mm plastic coil zipper. Replacing a slider on boots might be harder than on clothes, since the top end of the zipper might be integrated into the leather, so you have to open those seams first. And of course leather is less flexible than cloth. With some boots the top ends of the zipper can also have been melted to create a stop. Conclusion: take a good look at the zipper before you buy. But of course boots can be bought already locking as well; see for instance Refuse to be Usual.

Boots come are all sorts of lengths, up to and including boot pants and even heeled catsuits (and custom made at Miceli).