I am myself moving to doing get-ups with the 40 from the 32. After a few weeks, I came to the conclusion that there are 3 aspects to this:
1 - Programming
2 - Technique
3 - Getup variations.
I think I will not outdo
@Pavel Macek 1 and 3. I am not doing exactly what he suggests, but the idea is the same. I only go heavy once a week and do what I can in term of complete get-ups on that day. If it's only 2, it's only 2. I can also do partials on that day with the 40 (to tall sit and lunges). The other sessions are a mix of work with the 32, either continuous get-ups or doubles.
Regarding technique, I noticed that I must really ramp up the tension and keep it there for a successful heavy (to me) getup. I stayed with the 32 for a long time. I can easily do multiple doubles with that bell or do alternating get-ups with no rest, continuously, for more than 10 minutes. My body has learned that I can wave the tension at various stages to get a bit of rest here and there. However, there is no such thing when the bell gets heavy. I must be braced strongly through the whole movement. Things that help me are:
1 - Brace the "core". The whole breath behind the shield thing.
2 - Actively pull my shoulders in their pocket.
3 - When doing the difficult transitions (to elbow and the lunge), imagine you are gripping a post and pulling yourself up. That is, the unloaded side is also tensed. Your free fist should be closed as if you were gripping a post and you should really pull with the unloaded arm.
If I start the lift without maximal tension, the bell feels much heavier. From the moment I start moving the bell, all my body is tensed. If I don't do this, it's like my body thinks that I'm in trouble and that there is not enough strength to do the movement, so it tries to fool me into not even trying. If I'm really tense, my body feels safe and gives me the "go ahead". The bell feels lighter.