Attempt one: Using the entire spare bedroom as a "recording studio" failed. I used quilts, a matress pad, a bedspread, and sheets on all hard surfaces. I added an old egg-crate mattress around my laptop and Blue Yeti USB microphone. That did not deaden enough extraneous sounds. Plus, the room could not function in any other manner.
Attempt two: Shrinking the size of the "recording studio" to a corner of the room seemed like a good idea. Although it was slightly better, it was not sound proof enough for good recordings.
Attempt three: Using a closet. What about claustrophobia? I wouldn't know until I tried it. I was able to make space in a different closet for luggage that was stored in the spare-bedroom closet. Throwing away a few items, including useless, empty boxes, was painless. The closet was only three feet wide and I had no desk that would fit. I did have the adjustable stand for my music keyboard and a removable computer-keyboard shelf from a desk. Add one very small, folding chair. Perfect fit!
I used the same quilts, matress pad, bedspread, sheets, and egg-crate mattress on all surfaces, over, under, and side to side. Voilà! One small, 3' x 4.5' dead-sound room. Although it is not very pretty, it is effective. As for claustrophobia? The door knob is only 12" from my left shoulder, and I take frequent breaks from recording.