Welcome to the forums and I'll touch on your post briefly.

May I ask where you're from so I get an idea of the general temp.

Next several things you can do to up your heat besides using the over head lights. On my bigger tank I keep an UTH on both sides of the tank cool and warm, so that way the temperatures are set where I like them at.

Ideally you want to cool side to be around 82-83 and the warm side to be 88-90.

Have you ever considered getting a rack or maybe something to help raise your ambient room temperature?