One thing is to have a Betta which is in better condition too. Using Indian Almond leaves /IAL and other botanicals and DW will help with the condition of the Betta's body, because of the tannins. Betta's like tinted water and of course benefit from a better condtion / and wellness.
Also a Plakat Betta doesn't have the flowy fins of many other varieties and are fun and beautiful as well, more active as they aren't dragging a ball gown around. So maybe check them out.
Using a Betta Log (also check inside for any sharp protruding plastic edges jic) or floating stem plants will also help keep the fish from laying around on the bottom all the time, also can help avoid fin rot.
As for stones. I have used many types and even smaller sized Dragon stone. Using plants to shield the fish is a great idea. Petrified wood is pretty and usually smooth.
Moss, Anubias nana, Bucephalandra, Crypts at the corners of stones and DW. Subwassertang can be situated on or next to a stone.
Aquarium safe caulk or sealant might not look the best. But a scaper "tip" is to coat the edges of sealant with sprinkles of brown or same color as what you are using it on, sand or substrate to make it appear more natural. Also can add a bit of moss or other plant there.