My papa furnished the apartment for me, but the bed is incredibly uncomfortable.

I’m Kaz, a male member. Why not try telling him, “I keep waking up with a stiff neck, I’m not feeling rested, I have trouble falling asleep, and I wake up during the night”? The key, I think, is to simply explain the problem you’re currently having with your papa, rather than directly asking him to buy you something. If he doesn’t offer to buy you a replacement mattress, you can always buy one yourself. As I was writing this answer, I realized that when he chose the furniture he was going to buy for you, he didn’t ask for your opinion or choose it together with you. That’s a shame.

I’m Aya, a female member. I’ve had a similar experience, so I understand how you feel. In my case, it was the opposite of what happened to you. He actually said something unbelievable like, “Don’t you think we can do without a bed frame? Wouldn’t it be fine just to put the mattress on the floor and sleep?” I went along with it for a while, but it was honestly unbearable. The mattress may have been expensive, but sleeping that way was still really hard on me. I told him exactly how I felt: “Without a bed, it’s basically the same as sleeping directly on the floor! I want a bed. If you won’t buy me one, I’ll buy it myself.” I think he’ll probably just buy one for you normally. In fact, it seemed to irritate my papa (a male supporter) more when I paid for things myself.