Need to know context. Very unlikely a shoulder holster will be usefully concealed all the time, and it is quite likely to get in the way (at least chafe a lot) while using your arms for everything.
Probably: +1000 for the Wilderness Safepacker (or similar). A squared off nylon bag that looks like nothing unique. A pouch. A date book. maybe an equipment holder.
But... quickly opens and there's a pouch. Put the gun in loose or add a pocket holster sort of thing, spare mags, etc.
Safepackers were originally designed for wilderness rescue types, wearing rucks, harnesses, etc. and a holster was not a good fit, plus was visible so either freaked people out and had to be explained or bad people would literally try to grab for it. Plus, exposed to the elements, rocks, etc. So, this is safe, secure, and concealed while being well-nigh as easy to get to as a holster... well, an old timey flap holster at least.
For your purposes, I think of things like the seatbelt on your chair. Lots use safepackers when driving, and so on, so that may be comfortable and out of the way while still functionally on your body. I would try it out. Useful enough that it is gonna be a good backup at the least.
https://www.thewilderness.com/safepacker-concealment-holster/
If not, and you really, really want it directly on your upper body, then Hill People Gear kitbag
https://hillpeoplegear.com/Products/CategoryID/1/ProductID/2 are highly suggested. A bit odd looking to me, but just a bag on your upper chest, not a gun you have to worry about concealment garments with. Stable enough people run with them, etc. Several sizes and configurations. Beloved so do googling about them generally where you will see EDC forums, backpackers, etc ranting, don't need to just rely on the mfg site to describe.
Also, sometimes people hate them so they come up on the secondary market, maybe you can get it cheap on eBay.