We are staying at a Four Seasons hotel for a week. Just spent our first night, and we found that the mattress is not very supportive, i.e. it sinks in too much under our weight, and we didn't sleep well and ended up waking up with sore backs. (our weight is at the upper end of the normal range). If we were staying only for a night or two, we would just take it. But we have 6 more nights and can't really enjoy the vacation with sore backs every day. Is it acceptable to ask the hotel to change to a firmer mattress? If not, we might need to change hotel and pay the penalty of 1 night's room charge.

We haven't encountered such situations before, and would like to seek advice from the infinite wisdom of flyertalkers.