All the zabuton, cushions, mats and pads are pretty much the same. The nekos use them the same way.
The big cushion can fit 2 normal cats
The cats use the hammocks the same way as the cushions
On the fluffy bed:
The cats on the hot water bottle:
The cats on the royal bed:
Like the big cushion, the cubes can be put in a small location yet accommodate 2 cats so they’re quite worth it. The tree trunk with hole (stump house) and mushroom house/shiitake house too.
The nekos can sink into the soft cushions (dark brown, sheep, sakura mochi, hamburger or beads(bean bag),Mister Penguin) and look quite cute so you may want to get 1 of these.
The burger and hot cake cushions are slightly more versatile. Better to get the burger/hot cake cushion though as the extra poses for the dark brown cushion are similar to the poses for the hammock or cushion or zabuton.
The dome cushions, tents, macarons, egg beds and shu cream house are pretty similar. It’s hard to see much of the cats when they’re in the macarons though.
So you should get:
Special items: chirimen zabuton (red), sakura zabuton (pink), shirayuki zabuton (pale blue), high class cushion (green and gold), royal bed, big cushion, high class hammock, pyramid tent
1 of the cubes / tree stump house, burger / hot cake house, 1 of the dome cushions