The 10 inch is a great mattress for kids. Not the best you can get but a good first “big kid” bed (aka non-crib ) mattress for the price.
Will either work well with an adjustable bed?
Are these plush, firm or what?
Not sure about that. These have springs in them that might get all bent out of whack or misaligned on an adjustable frame…
For the adjustable bed, the consensus on Amazon seems to be no as it could cause a problem with the coils.
For the 10" per Amazon:
For the 8" Per Amazon:
Medium-Firm Feel - This 8 inch twin xl mattress is orthopaedic designed, no matter how you sleep, it will create a comfortable cushion medium firm feel, providing perfect comfortable sleeping experience.
There is no universal rating for “firmness”; it’s all relative to other mattresses in the same line and otherwise a purely subjective marketing thing. With innersprings it’s mostly a matter of how much soft padding they add on top of the springs, which otherwise remain the same across the line – less padding conforms less to the body and counts as more “firm” than more padding that conforms better and counts as “plush”.
In this particular case, I’d reckon the 8" without memory foam would probably count as more “firm” than the relatively “plusher” 10" with memory foam. Also note these come vacuum-compressed, rolled up in shrink wrap and boxed for shipment, so the edges won’t be as firm as mattresses delivered flat can be.
All that said, I got one of these 10" models last round for a 5’8" full-figured ladyfriend with a degenerative spinal condition, and so far, she absolutely loves it and has been sleeping better with less back pain than before.