I'd recommend getting an under-bed storage box for the litter tray, perfect size for them to sit in.
People usually put in second levels, I wish I could but I'm rubbish at DIY and it's taking me a while to figure out how. So for now they have foot stools with a towel draped over it to create a hidey space. I also got some tarpaulin from Poundland and made a sort of skirt around it, to keep as much mess as possible inside.