Sora works flawless for me. It's "9 speed", but makes no difference. If you want to pay more, get lighter, you could look at older 105 (10 speed) (for the rear at least), or get a 9 speed MTB derailleur for rear.

For the front, because of cage width, I'd look for an older "8 speed" Sora, or new Claris. They should work fine.


P.S. I swapped 5700 105 setup (10 speed) for an 8 speed setup with Claris STI-s, and Sora derailleurs. Shifting has improved - faster, more precise. 8 speed has enough margin for shifting errors, so it works fine with the cheapest shifters/derailleurs.