Appropriate door stopper for cat introductions?

I have a 1 year old cat and a 4 month old kitten i’ve been trying to introduce. So far so good, but now they’re at the stage where they’re ready for some visual contact. I live alone and can’t install a heavy tall gate on my own, so I’m wondering if there’s a door stopper that can keep the door open small enough where they both can’t come in but can still see and smell each other?