Here's a YW search for 20-24 foot daysailers in the PNW and CA... some interesting ideas here.. some of these come with trailers.
Most will have more accommodation than you're looking for and many will have fixed keels or excessive draft for trailering, but this will give you an idea of what's on the market.
Something like an SJ 21 or C22 will probably provide most of what you're after and give you the option of overnighting on occasion.
If you're budget allows the Harbor 20s on this list look like fun, but I don't think they are available with a swing keel. From their class site, though, it seems many live on trailers...
In fact a search with 'swing keel' as a key word for the same area turned up zero results.
(Sail) Daysailer Boats For Sale