Lake of the Ozarks State Park in Missouri has boat slips in the park, right next to the campground, that will accommodate your 26' cruiser, and a very good launch ramp right at the little state park marina. If you can go in the next 6 weeks or so, it is beautiful boating on that lake after Labor Day. Our favorite time there was fall boating, after most of the tourists left...otherwise, that lake is pretty crowded.
Also, Kentucky Dam marina on Kentucky Lake is very nice. Campground is about 2 to 3 miles away from the marina, and the sites are just a little tight to back into (no angle, have to back in 90 degrees from the road) but it is a great lake to boat on.
Finally, also on Kentucky Lake, but further south, the Tennessee State Parks are very nice, and many of them have marinas and launch ramps.
Enjoy!