Keep using the 20 bell for another month or 2. Build a pattern of success with that volume. Then move up. The problem with jumping immediately to the 24 is that, in all likelihood, you're going to be hard pressed (pardon the pun) to even finish medium day. That can be discouraging. A bad day after doing the 20, once or twice (not enough rest, not enough food, not feeling your best) and you'll get discouraged. That's why you should own it. 4-8 weeks of success. You can always do the first rung or two with the 24 if you want to break in.
When you start using the 24 and let's say you're ladder looks like this. 1,2,3,3,2. You missed 4 reps. Just do 2 more sets of two to get to 15 then start the next ladder. Each time you get to 75 on each side with less sets, you're getting stronger.
I'm a big fan of owning the bell before moving up. I can do the 32 kg, for all 5 ladders. Don't own a 36, but am buying one soon. My plan until I buy one around cyber Monday, is to only clean it once and then do all the presses, or lower the weight sooner. Or change the rung/rep scheme.
