.. hmmm... and here you blew yourself. Upright with a possibility to play in tune where you move your fingers slightly? it's only the open strings that would give away some out of tune-ness...the upright are fretless and, thus, except for open strings, are always in whatever tune your fingers are playing. Other solutions: Well don't play any upright then. You don't have an acoustic cembalo player do you?my upright needs little nudges and tweaks — even a set break is enough to disrupt the tuning, the strings cooling on the break and then encountering warm hands after sitting under the blast of air-con.
My headless doens't drift at all once tuned up. If it should, I can actually reach for the tuners which resides at the bridge WHILE I am playing even busy stuff too, to fine tune one or two strings if needed. If the strings' too sharp, if the strings too flat I just bend them up a bit. Down if it's a low E-string. But generally speaking strings goes up, when they drift out of tune. Yes, the neck being graphite sure helps, but the headless is the main crucial point of why strings don't go out of tune once tuned up. If I have to change strings to a brand new set, just tune them up, after less than 5 minutes adjusting for standard tuning THEY STAY THAT WAY, during the gig. They don't slack and drift. All headstocked basses will do, and you have to adjust ever so often, just after a couple of days it will stay put.
But I agree, those self tuning mechanism aren't any good, you have to stop playing mute the bass/guitar, and then press button. Well, I agree THOSE self tuners are very expensive. It's that they drift while playing that's the main problem...and for those ones there's this solutions (albeit more expensive than most tuners):
https://evertune.com/shop/index.php
Alas not for bass as of yet. Probably because they think it's not needed.