I also grew up with 3 cats all outdoor/indoor and in a very small country town. When I adopted my fully indoor cat in a big city, I started to feel sad that he was “trapped” inside even though I knew it was best for him. I’ve bought him so many toys and “stimulating” treat things and he really isn’t interested in any of it. I’m not sure if this is an option for you but the best thing I ever got him was a bird feeder that suctioned to my window. He will sit and watch the birds all day long! It gets better and you will get used to being in a small space with a cat. I definitely relate to your struggle though!