I know hand carded wool would pack down and also form lumps. You would end up sleeping in a bowl. I wouldn't use it, especially at that price.
I got a standard twin mattress for our camper last year for $99 and tax. Larger sizes weren't much more. If you watch sales and go for the budget styles or mismatched sets, mattresses are pretty inexpensive now. You don't really need a box spring either. Our bed sits on a platform I made using a drawer base from a waterbed. I use the drawers to store bedding. Our mattress rests on OSB on top the drawer base. Personally, I consider box springs useless and a waste of perfectly good storage space.