IMHO the only use for a Collar, is to hang their ID on. When I get a new Puppy, it gets both Collar and Harness on it 24/7 until it is house broken. Then the Collar stays, and I put the Harness on it, when we go out to walk/jog/whatever.
I've found a full time Harness (when they are Puppies) is a super good tool to handle them with. It's so easy to just hook a finger in it, when they are on your lap and haven't established "distance" and try to jump. It's also a very good "handle" to control them with at other times without having to use two hands.
I always use a Harness and Leash/Reel when going anywhere. This gets them used to being close at all times. I can't find the exact size I use for Puppies, and, have altered a collar/harness set for repeated/hand me down use. Below is a reference to the type. Quite secure, washable, and can be altered easily.
Ref:
Grreat Choice™ Perfect Fit Adjustable Harness - Harnesses - Collars, Harnesses & Leashes - PetSmart