I'm also coming from the double bass and for many years I played a very "upright-like" acoustic bass guitar that never worked well for me in a horizontal position mainly due to its depth and highly radiused fingerboard. After much experimenting I found a fully upright position to be impractical for a couple of reasons. A) it kinda requires an endpin to really pull off well otherwise you really end up reaching for the low notes and B) it's not that bio-mechanically useful with a bass guitar. Without the upper bout to control the bass with your hips you end up using your left hand which creates obvious issues. I found a more classical guitar 45 degree-ish kind of approach to work well and over a number of years experimented with straps, footstools and support devises to achieve this.
Straps are dependent on the location of where the buttons attach to the body and are not a very flexible solution. If it works for you great but it never did for me.
Footstools are generally inexpensive, readily available and do work but like a lot of people I didn't like the asymmetry of the hips they cause. They also don't work with a high stool.
A "guitar support" was the solution for me and I tried almost everything available at the time which was well over ten models. Pictured here is the Ergoplay which was very solid and I liked a lot. The
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One that came out after I parted with this bass and I've not tried is the
Kris Barnett Adjustable Magnetic Guitar Support. It looks very similar in function to the Ergoplay and is designed to attach with magnets inside the body. You could easily experiment with rare earth magnets attached to your bass with double sided tape and there's flexible magnetic strip stuff out there too for a more clean, compact install. With a little messing around you could install just about any available support with magnets.
Here are a
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Honestly though after all this I've found with a solidbody bass guitar played at 20-30 degrees and raising the strap to where I have comfortable access to the whole fingerboard works as well as anything. At some point I accepted that in many ways the bass guitar has different bio-mechanical issues to overcome than the double bass does and just accepted it for what it is.