I'm not sure you can quantify the chances of being able to get the bedding you want vs. not. It depends on a variety of factors, not the least of which is availability of rooms that fit your needs. They could even tell you in advance that you'll get the bedding you want, only to arrive and they'll be "sold out" of those rooms, and you're stuck.

That said, it might actually still work out cheaper or approximately the same price-wise as what you're currently booked at to bid for two rooms instead of one.