I would still reccomend a heater they are really helpful. What is the tank size and are there lots of hiding spots sorry if I did not see it and its in there.
He has been in a 3 gallon tank.
I've kept him in the exact same tank at my place.
He has a little house down the bottom that I am told he has always had and he likes to pop in and out of there, especially likes to sleep in there.
There is a little penny wort plant on top of the house.
And there is a fake floating lily that I have been told he likes to make bubble nests under.
I can see that at present there is not enough hiding, playing or resting space scattered inside the main space of the tank though as the shape of the tank means the base is quite small and fits only the sleeping house and the penny wort that sits on top of the house is too small to provide 'near surface' resting spots or for him to play/hide between foliage etc.
So I have today placed an online order for a few new things to switch around and experiment with which will hopefully arrive in about two weeks:
Exercise floating mirror
Mini floating betta log with feeding hole
Different types of floating lily options
Variety of different types and sizes of silk plants to try out
Seachem stress guard
And I am going to keep an eye out for a different little sleeping house to sit on the bottom where his current one is that he really likes, just in case something about the shape or colour of the current one is upsetting to him.