How "nicely" do you want it to fit? Do you have a hardtop? Most of the over-the-counter styles are probably not going to work very well while your boat is in the slip - which you mentioned is your goal. They'll end up being loose fitting and/or the tie downs will be to close too the water.
Besides, OTC covers won't have the slits in them for your cleats... which of course you need.
Ideally - find a local company and have one custom made. Maybe you'd want it made in two pieces that zipper together? Maybe you want a zipper door sewn in? Having a ratchet strap sewn into the hem to tighten it is the way to go - makes it very tight and EASY to secure. Of course, a custom cover is going to cost more - but then you'll end up with not only a better quality cover, but also better fitting and easier to use cover.