Belly Bandit Sizing

PetNurse10

I'm jumping over from 3rd trimester wondering sizing on belly bandits for any of you that have used them.  I'm 35 weeks and measuring 43" around which would put me at Medium (38-43") according to their website. 

My question is... I've seen that a lot of people say they shrink out of their first size really fast (like a couple weeks??).  So I'm wondering if I should a) get the small size to begin with and just wait a little bit to start wearing it or b) get a cheaper medical grade binder for the first few weeks and then wear the smaller belly bandit.  I just don't want to spend $100 on two of them, but I also don't want to take the chance of it not working well if I don't.  Any thoughts would be greatly appreciated!!!  TIA!