Personally, I'd stick with the bigger room and those nice ceilings. That depends upon the room shape and size, of course. The smaller room may be better shaped (rectangle not square). Just listen to it. Then buy a small can of Dap or other filler and tell your mother you only need to put in two nails. Show her the Dap - it is easy to use. You can use a butter knife to fill in the holes if you don't have the right tool, just be sure to clean the knife before the dap hardens (and bless your mom's training, she's prepping you for a spouse).
Use some twine or wire to hang your blanket in the corner and you can take it down whenever you aren't recording (or mixing if it makes that much difference). The blanket should be behind you for the vocal recording, so you are singing toward the middle of the room and the blanket is helping absorb the reflections of your voice before they can bounce off the wall behind you and get picked up from the microphone's sensitive side you are singing into. A cardioid (heart)- pattern mic will dull and attenuate the sound coming in from the sides and rear (but not eliminate).
If your studio space has a bed, bookcase etc. it should help even out the bass response. Walk around and clap and listen for the different reverb to get a good idea where to place the mic. Traditionally, the middle of the room is the worst, but in my humble little space off the center (just outside the ring of the ceiling fan) provides a very nice sound.
Good luck. And if one room doesn't work, pull the nails and use the dap, move the bed and start in the other room.
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