Lots of good advice here. I’ve owned KHS, Santana, and Co-Motion, my favorite has been the Co-Motion Speedster. A light bike, moderate cost and good stiffness. Chris is so right about fit,fit,fit. Often you see the forward rider reaching for the bars with good weight distribution but the rear rider is sitting upright a la beach cruiser. A stem and bar combo that allows the rear rider a fit like their single made a huge difference for us. The rear rider reaching for the bar and tipped forward a bit gives an easier posture for power plus the head/shoulder mass is not directly over the saddle easing the bumps somewhat. Santana makes their own extra wide drop bar to clear the front guy and still create reach for the back guy. My Co-Motion used a bullhorn style bar in the rear and that works well also. A good fit will also make standing easier, with some practice and a decent frame you can be smooth and seamless. As mentioned before we tend to stay planted but if you can stand confidently then you can build stand breaks into your ride for a litt!e more comfort. Good luck with your search.