pond snails are the best for fig 8's IMHO and quite easy to breed. Make sure you take good care of them and feed them well so they're more nutritios for your puffers. Many also breed ramshorns, although i have limited experience with them.
I'm currently breeding pond snails, well attempting to. They're just not multiplying much. I'm wondering if the trumpet snails have out competed them... I'm considering removing a sizable chunck of the trumpet community from the breeding tanks (which are our fresh water fish tanks)
Yes, Malaysian trumpets are not good for puffers, they cause chipped teeth, and will out compete pond snails. You don't NEED a heater to breed pond snails, it just slows the process down.
Edit:
I mean, not having a heater slows things down...having a heater speeds breeding up.
My Puffers: Puffers I have kept: T lineatus T miurus A modestus T biocellatus C valentini C coranata C papuan C lorteti DPs suvattii burrfish T niphobles
I said trumpets are NOT good. Too hard. Pond snails are good, and like I said before, ramshorns are good too, I just have limited experience with them.