tank mates for bettas?

hi all! my betta sadly died about a year ago now (he was called Boleslaw and he was so beautiful and i miss him alot). Ive been missing him as my little companion in my room because theyre such beautiful fish and also i need someone/something to talk to at weird hours of the night haha.

i plan on taking my time with the tank setup to make sure i get it right. i bought a ~40L tank to set up, and ive been looking at plants. i have a few ideas about what i would like to get for those (but i am happy for suggestions if anyone has any easy maintenance plants in their tank that they really love) but what im stuck on at the moment is tank mates.

i would like to put something live in the tank before i introduce my betta to it, and im not really sure about what i should put in there, and if there really are any suitable fish to put in with them? if anyone has tank mates for their betta that are reasonably low maintenance, id love to know what they are. if it makes any difference to the sort of tank mates i can have, i am located in Australia.

thanks in advance for any help :)