Generally speaking, some just starting out with full time diaper use is going to be emptying a nearly full bladder when they do pee. This means you will need a very thick diaper that can handle floodings pretty well.
Start off with a fiaper you believe will be way more capable than you need. If it turns out to be too much thren you can always cut back. However, start out with too little of a diaper and you will end up with lots of leaks.
Also, the thicker premium diapers tend to be cheaper overall because you'll need to change less. Cheaper diapers may seem like a better deal, but their added changes (and boosters) only multiply their cost when looked at on a cost per day basis.
I'd recommend Northshore Supreme, Confidry 24/7, or (my favorite) Betterdry.