The easiest thing I can think of that would remind *you* of Middle-Earth without overwhelming your siblings, would be to think the way elves think, and make the room as *natural* as possible. Think of (subtly) turning it into a forest, or a garden. Soft greens, quiet browns, sky-blues up high.
Add some good-sized plants if you can (does it have any windows, enough light for plants? A few potted flowers would be lovely.) Add an indoor fountain if you can.
Your sibs should probably be able to deal with a fwe elvish artifacts, and for you that should complete the effect.
If you have any instruments that could pass as elvish, they'll help--you can always play them
You could also add some Celtic- or Indian-print sarongs.