OP here. Thanks for the replies folks. I had actually typed up a longer thread starter, but thought to myself - "nobody wants to read my life story". But here's a bit of background.
I'm a recent cyclist, not unhealthy but not athlete fit either.
The bike I ride is my first derailleur bike, before that I rode hub gear bikes. I built this bike myself, it's a touring frame, which I bought with the idea of maybe doing some light touring (Covid stopped that), but mainly because I like the idea of being able to attach racks, carry stuff, and I also like the low, steady geometry. It's got drop bars. It's got 48-38-26 with a 11-34 cassette. And I use all the range.
I built it up with a triple, originally Sora, drive train, but have now changed to Ultegra 6510 shifters, 9 speed triple. As those are old shifters, and 9 speed triple is on the way out, I've been busy building up a stock of "backup" parts, if I see any NOS or good used shifters/derailleurs etc.
The good thing about that generation of drive train components is that there's a lot of compatibility - Ultegra/105/Tiagra from that time is largely mix and match, 9 speed road and MTB can be mixed, and so on. And a big one is that the STIs for the front are double/triple.
So as I've got a lot of "spares" I could build myself a double, using a suitable frame. Maybe a lighter non-touring frame. I was wondering what the benefit might be. A bit less weight, which might mean I wouldn't need the very bottom gears as much, maybe.