The bedroom can be effective vocal booth. Simply open up all the closets wide (assuming they're stuffed with clothes). Pick one of the closets and put your mic stand against the clothes and have the mic just a little bit away from the clothes. You stand in the bedroom facing the closet and sing into the mic. When you sing towards the closet, about half of your voice will be absorbed by the clothes. The rest will bounce around the room, but a good chunk of it will find the other closet, the bed, and other absorptive materials. The reflections that actually make it back to the make are minimal, so you should have a workably dry vox track.