Originally Posted by Bianchiriderlon
The seat is very uncomfortable. It is hard to detect just how uncomfortable until the bike is ridden for some distance. It is ok starting out, but by the time I’ve gone 10-12 km, my lower back and hips begins to ache. Had this been apparent at the time I was considering the purchase, I may have given the bike a pass.
I hate to break this to you, but with these semi-recumbent designs, in my opinion you get the worst of both upright and recumbent worlds: your riding position doesn't allow you to get off the saddle to take weight off the bike to jump over curbs, shift your center of gravity or honk on the pedals, and it's obvious you sit with all your weight on the wrong part of your posterior (the muscles, instead of the sit bones on a regular saddle), you have no back support and you have to bend forward, so it doesn't justify giving up the few advantages of an upright. It's no surprise that your hips and lower back ache after a while, pedalling while bending forward without back support. There's a reason they're marketted for short distances only. It looks as uncomfortable as those cruisers with monkey bars, long fork and chrome everywhere, but at least with the cruisers you know where the emphasis is, and it's not comfort, it's looks.
I was wondering if a BikeE seat may fit
It won't, unless you're handy with a milling machine and files. The BikeE seat is mounted on the square boom's top rail with 4 sliding plastic clamps and two QR skewers. You'd have to manufacture an adapter to fit it to your bike.
If so, I am not certain that they are still available as I have heard that BikeE is no more. I may try a conventional seat on there and see how it fares. Any advice would be welcomed.
One thing you could try is weld an extension to the stunted back support and attach a proper seat back on it. Maybe you can bolt the extension instead of welding it, maybe you'd need bracings for additional solidity, I don't know, and I can't tell how solid it is there from your photo. With a real seat back, you'd be able to rest your back against it and, I think, almost eliminate back pains.
I don't like to be so blunt, but frankly if I were you, I'd sell the bike while it's new and still has resale value and get a cheap CLWB instead, with a proper riding position. I'm not sure it's worth the effort of upgrading it...