I would recommend making your own decorations just for safety measures.
Many times have I considered petsmart/petco decorations only to feel the inside and pretty much prick or cut myself on it.
I know if it cuts me, it'll definitely do some harm to a betta.
Some of the "homemade" toys you could consider are a coffee mug thoroughly rinsed of soap or other chemical traces, a terra cotta pot with the hole at the bottom enlarged or removed and possibly extra holes added to the sides (ensuring to sand/dremel all edges smooth), or you can buy a sheet of craft mesh and cut and tie it together into a cave or tunnel shape and tie moss plants or glue silk plants (with aquariumsafe silicone) onto it.
If you use the craft mesh be sure to trim off any spikes and maybe file it smooth with a nail file if you want (i spent an hour filing away at trimmed spikes for extra safety)