I can think of a few other options.
The Green from Green River to Spanish Bottom is an excellent Class I run with a riffle or two, easy to get a permit, 120 miles. The 54 miles from Green River to Mineral Bottom doesn't even require a permit. Lots of water at this time of year. Lots of archaeological stuff in the Canyonlands section. Drawback is that if you run to Spanish Bottom, you either need to get a jet boat out (book early) or run Cataract.
Gunnison from Delta to Whitewater is usually Class I-II. You could run 2-3 days here, maybe continue downriver.
Upper Colorado from Pumphouse downstream can be at least 2-3 days. You could continue down as far as Dotsero if you wanted to add days. Good flows, perhaps II-III at this level.
San Juan above Sand Island does not require a permit, but there are a couple of diversion dams, so not suitable for rafts.
If you want to sea kayak on flat water, you can go explore canyons on Reservoir Powell. I did not think this was a fantastic trip, but I know others have really enjoyed it.