My rule of thumb for 26" wheels is that the sprocket should have half the teeth of the chainring (23 in your case). This is a good ratio for cruising around casually, but won't give you a lot of top-speed. Let's have some more opinions, 'cos I'm a wimp on single-speeds.
Doesn't have to be exact, 22ts are easy to find, someone on ebay has 'em for a couple of bucks a piece from KT(but I think they advertize them as Strumeys) who is a big maker of rear hubs for cruisers. They fit most modern hubs, shimanos etc.