Sorry that I can't help since I already choose a roommate but you should be find getting a wellness apartment.
Did you sign up for room mate matching if you can't find someone then Disney will match you with someone who wants a wellness room as well?
What are your program dates? Remember only people coming and going on the same day can room together. So it would be helpful to post that.
I think "availability" in this sense is that they will try to put you with another 23 year old but if there are no over 21 people who want wellness you would be put with under 21. Also to my knowledge all apartments, wellness and non-wellnes, are smoke free and so wellness does not guarantee that the people in your apartment won't smoke outside of the apartment it only guarantees no alcohol in the apartment.