Have you considered a comfort bike? Upright and usually with low gearing. I turned my old mountain bike into a cruiser simply by changing the saddle to a Cloud 9 and the handlebar to a cruiser bar that is wide with lots of back sweep, just like the good old balloon tire bikes of the 60's. Super comfortable on 5-10 mile commutes and will easily go 20 miles without fatigue. I have 1.75 Kenda smooth type tires on it, but have run 1.5 Nimbus tires as well. No pain, no strain.