That would be fine-but the issue might be getting a sub with the performance you want that will fit under the bed.
Home theaters come in all shapes and sizes and levels of performance.
We have one customer who has one in his bedroom and uses 2 of the DTS10 subs.
DTS10 | Danley Sounds Labs | Danley Sound Labs, Inc.
1 is usually overkill for most regular home theaters-but some of these guys are a bit on the "insane"side when it comes to subs. 40-50Kw of power is not all that unusual for power for a home theater sub.
We have another guy who has a small (12'x14') bedroom that has a Danley BC412 on either side of the bed-because he wants lots of "impact" and punch.
BC412 | Danley Sound Labs, Inc.
So the usual answer is "it depends".
Suggestions about where to put it in your room REALLY depend on what the room looks like. Not all bedrooms are the same.