My most recently-bought hides came from Reptile Basics. I estimate the size: obviously you don't want to replace all the time when they grow a little, & since
BPs prefer a snug-feel, you can stuff some paper towels or something inside to make them feel "cozy" while the snake grows into them.

I prefer glass bowls (because cheap plastics leach chemicals into water) & I often get some nice flat-bottomed heavy (tip resistant) bowls from thrift stores.