I agree with the others that you should be able to handle this by yourself, and think it's great that you want to take it on.
For point of comparison, I'm a 60-year-old man and not what you would call "strapping." I launch, sail and retrieve my 19-foot 850 pound Flying Scot by myself. Getting the boat back on the trailer if there's a cross wind can be something of a wrestling match, but you'll be surprised at how often someone at the ramp will be willing to help out if asked ... or even volunteer. A simple "Hey, would you mind pulling the stern line so I can get lined up on the trailer?" and the offer of a beer afterward has led me to meet some nice people.
Also agree that rigging the boat solo may be a bigger issue than launching. Just be sure the type of boat you're looking at has a deck hinge for stepping the mast or some other system for doing that by yourself. Most small boats will ... but be sure.