I also just use the floor. We used the changing pad till we moved him to the floor at about 10 months. We were using a receiving blanket at first, but now just the floor. While the changing pad is nice, it isn't necessary, and could save you room to not have it.
The other option, since you do have a kind size bed, is to use a corner of that with a towel or receiving blanket. There are some waterproof receiving-type blankets, just in case.