If you can't clean up the painted edge, you could always add a 1x3 piece of wood as molding. You can even carry it up to the ceiling to frame that wallpaper. I don't see that paint color in the wallpaper, or maybe it's a lighter version of the flower centers. Maybe stencil on a design using the darker color, or another color from the wallpaper to help tie it together. Then narrow floating shelves or vertical frames or something in the painted areas it you feel you need it. Maybe turn the bed around so the wallpaper is the headboard.

No such thing as wallpaper for floors, but there are a few good solutions for water resistant flooring. Pvc, vinyl, linoleum, epoxy or polyurethane paint, for example. I see you live in India, I have no idea what products can be bought there.

Can you explain what spacer tiles are? Without knowing what they are, I should mention that wallpaper always needs to be applied to a flat smooth surface, over top of a layer of sizing to help it stick.

Cost is a factor also between papering and paint. 20 years ago, I painted and wallpapered everything myself. 10 years ago when I moved and bought a condo, I hired the papering and I did the painting. Last year when I downsized, my handyman and I just did the painting. No paper. I have found that at my age papering is too much for me. When I get down I can't get up and when I am up it feels too good to get down :>)