even in a 10g it is all dependent on what you like and how much cleaning you want to do. I have had gravel, stones, sand and bare bottom in various tanks over the years and for a betta...I prefer bare bottom.
you can get weighted silk plants that look very nice, toss in a hidey hole or 2 and a few glass stones or nice rocks and your tank will look beautiful AND be super easy to keep clean.
right now I have gravel in my 10 g and as soon as the pleco moves to the larger tank, it is all coming out. (or sooner if I get sick of cleaning it)
cleaning a bare bottom is easy with a turkey baster to suck out any poop daily and with a good filter I do 2-25% water changes/week and my ammonia stays at 0ppm
but that is just my two cents...and welcome to the wonderful experience of betta keeping Jacqui