Lots of great frame recommendations here already, but I think some of your best options would be available only as framesets, not complete bikes. Don’t let that stop you, getting a frameset and building it up yourself is the best way to get a bike that’s just right for you!
You say you’re a reasonable bike mechanic, so you’re probably more skilled than I was the first time I built up a bike frame. I started with relatively little knowledge and have done a couple of builds now, and I’ve learned that selecting the right frameset and components can make the build a lot easier:
- You want a frameset that takes a threaded, external bottom bracket (preferably BSA, I’ve also done a T47 build but the thin flanges are a lot harder to work with). Installing these is pretty easy if you have a large torque wrench, especially into a steel, aluminum, or titanium frame.
- Find a frameset that doesn’t require you to press headset cups in yourself. This requires somewhat pricy equipment if you want to do it right. It’s also possible to screw it up and damage your frame, so I find it’s best avoided. Some frames come with cups already pressed in, which is great.
- Avoid integrated cable routing running through the headset. You already mentioned you don’t want an integrated cockpit, so that’s good. Routing brake hoses through frames is pretty doable, routing through handlebar/stem combos and then through headset is not a good idea for your first bike build.
- Get a groupset with wireless shifting! It’s so easy to set a bike up with smooth and reliable shifting now, because all the parts just bolt on, everything is aligned much better because of thru-axles, and I find that things like limit screws etc. are much easier to work with than they used to be 10+ years ago. Youtube videos are also immensely helpful for learning how to fix any setup issues you run into.
- Don’t be afraid of setting up hydraulic disc brakes yourself. If you get a frame with entirely external routing (like a Fairlight Strael) you may not even have to cut any brake hoses during install (groupsets often come with brake hoses already connecting the lever to the caliper, and prefilled with brake fluid. If you do have to cut hoses to size for your build, just buy a good hose cutter and a brake bleed kit that’s specific to your groupset (I find the SRAM ones really nice, but they’re not compatible across manufacturers) and watch some Youtube videos to learn how to use it.
Sorry about the wall of text. I’m sure not everyone will agree with all of the above, but my main point is that if you pick a frameset that’s easy to work on, building up your own bike is quite fun and really not that hard.