I think a white mirror would work really well with the color of your wallpaper.
I am partial to bamboo mirrors right now. They just look really chic and happy.
I have found tons out and about at different thrift stores in my area, so if you can't afford a new one keep your eyes out for an older one and just spray paint it glossy white.
As for your sconces, I say don't be afraid to use what you love.
This ornate and large chandelier looks fantastic with a pair of simple sconces.
I think its a killer combination.
Something like this sconce with a small, pretty clear crystal ball detail would go great with your light fixture and keep it looking crisp and clean.
One of my favorite pair of sconces from one of my fave resources...check them out.
Let me know if you have more questions for sources...I'd be happy to help.
Good luck decorating Elizabeth and send pics when you are finished!!!!!