OK - first, welcome to the forum & welcome to the wonderful world of bettas! :)
What you have is called a drum bowl (because of the flat sides). I own 2 of the 2 gals. and they work very well for a single betta, IMO. I would not add a snail, however, because they are regular little poop machines - LOL!!! You are FAR better off doing your water changes than trying to depend on a snail to clean up (if that is your thinking in getting a snail).
A submersible, adjustable in the tank heater is the way to go, IMO/E. They are made to go in the tank/bowl and there is no fire hazard. The Elite Mini Submersible 25w is a TERRIFIC little heater that works well & won't take up a ton of space. I own one, have another on order (because I am so impressed with the first one), and know a number of posters here use them & like them. You can use them either vertically or horizontally - myself, I like my submersible heaters in the horizontal position.
Again - NO fire hazard!!!! :)
If you like, you can even add a small internal filter to a 2 gal. drum bowl! :)
Here is a good site, IMO, with good prices - they ARE a tick slow in the shipping dept., but the prices are pretty good:
Hope that helps and, again, WELCOME!!!