If you're looking for a room with a bathroom, then Yosemite accommodations in the park are hard to get - they start accepting room reservations 366 days in advance, and usually there's nothing with a bathroom left by mid-day. If you're willing to rough it a bit, and go with a tent cabin or a hard-sided cabin without bath, then it's a lot easier, and less expensive, and those usually have availability right up until you arrive. You can always book something like that and then keep calling back (or looking on the internet) in case another room opens up for your dates.
Otherwise, as the PP stated, your best bet is outside the park, either in Fish Camp or El Portal - I think there are more choices (both in terms of quality and price) at El Portal - Fish Camp is more high-end.