There are tons of papers available that would go with your midcentury home. Many people tire of a paper quicker than they are ready to redecorate and they can also look dated in a couple of years. Metallic papers were big im midcentury...perhaps a metallic silver paper? Are you also considering paint? You can get it in so many textures and a blue wall to match the blue in your loveseat would be lovely with some midcentury art and sculpture, or photographs on it. A mirrored wall with or without art or sculpture would also work with midcentury. These treatments are easier to adapt should you wish to change the look slightly from time to time. I would suggest replacing your stairrail with chrome or acrylic if that is in the budget...see how well the loveseat frame looks with the fabric? I hope you will post the "after" photos for us to see. Above all, enjoy the process!

It's refreshing to see nautical, navy BLUE. Everyone is saying the same thing for the most part - just introduce another color, definitely bright (yellow or orange IMO) and it will make it more current. What I really like is how your style will withstand the test of time - and with minor updates now and then it will always look fresh and "current".

This made me laugh: http://www.theguardian.com/environment/2016/jun/09/seagull-turns-orange-after-falling-into-vat-of-chicken-tikka-masala I couldn't copy the picture, but it's hilarious.

Personally , I wouldn't use that wallpaper -- it doesn't suit the apartment style IMO . I assume she wanted to add some focus and colour , but to me it doesn't work . To make it work ( or at least not 'jar' ) if she does insist on the wallpaper , pick out the burgundy or red of the wattle flower ( or whatever it is ) , and do a wall opposite it in that exact same shade , or maybe the kitchen area if you have good masking skills . The animal skin rugs look great , but the couch is 'lost' -- add cushions in the same red or burgundy as the wall , or go even brighter red or burgundy . Rest of the walls can be left as they are ( depending on wall condition ) or any similar neutral ( aka bland ) grey or cream , or possibly even a light steel blue .