Lot to unpack here.
Older Butteflies are great but the new mold ones are AMAZING. I highly recommend finding one. Check here if you need help identifying them:
For string I prefer poly. I use whatever poly I have on hand. Right now it’s OTS Normal, in the past it’s been Kitty Fat, Kitty Normal, and Alphaline.
I do not find that I need to change the string after a few hours of play usually. I also play 2A and there are some 2A players that will change strings after a half hour of play 
I would recommend trying a different poly. I prefer poly on steel axles over cotton.