If you want an "annual" ownership, be patient and wait. I would not buy two biennial weeks to make it annual, because you will pay two closing costs, and total MF of two biennial can be more expensive than one annual ownership. Also, when you decide to sell them later in any case, selling one contract is easier than selling two contracts.
I do own 3 biennial weeks, because I prefer biennial ownership for them. I use 2 of them myself and it's far from my home, so I cannot visit there every year. By owning biennial week, I don't have to worry about rent every other year and I pay MF only when I use them. My Marriott week is biennial and it is lock-off room which means I can have two weeks of exchange through II, and it fits my need. I already have other annual II exchangers, so I wanted biennial Marriott exchanger for Marriott priority.
For some owners, biennial weeks make sense, but if you want annual, try to buy annual.