Cat Door

I have a 10 year old female cat and my son recently rescued a 3 year old male. Both are spayed/neutered. We kept them separate for a few weeks then introduced them. The male Chunky constantly goes after the female Licorice. He's about 2.5 times her size and could really hurt her. It's not gotten that far but I'm worried it might. Chunky is locked in my son's room when we're gone and when he goes after her too much. I feel bad keeping him locked up but I cant handle the fighting. I'd like to get some kind of screen door for my son's room so the cats could maybe get used to each other through it. But I can't find anything like an indoor screen door. They have the full pet door w the metal bars but my son is 6'3 and it would be a tight fit for him coming and going. Any suggestions? Any advice is welcome on either getting the cats used to each or the door issue.