Am I asking too much or is he being selfish?

So my boyfriend and I sleep in different rooms because he is the loudest snorer and I am the lightest sleeper ever. I’ve tried everything like ear plugs, sleep meds etc. We’ve been living at his family’s second level in the house and we pay the same rent there. I want to order myself a mattress because for the past several months I’ve been sleeping on this nasty bean bag that’s flat and lumpy and hurts my back. When I told him I was going to order a mattress, he objected and said “no that’s too big.” (I want a king, because I’ve had a twin my whole life and finally have the money to treat myself). I will be paying for it myself, and assembling it myself and there’s plenty of room because. He says I should just sleep with him if I want to sleep in a real bed. I told him its not about him and I would if I could actually sleep. He still refuses and keeps telling me I can’t order one. Am I asking too much or is he being stupid?