You seem discouraged. Don't be. Finding the right carry solution can take a lot of work. A lot of us have faced this challenge. There's a reason we sometimes joke about "the holster box" at the back of the closet.
Here are some things to consider based on what you've said:
Pocket carry is quick and convenient. I carry an LCR that way a lot of the time. The real trouble with this, besides using up a pocket, is that it's hard to draw while seated. It sounds like a big issue for you is being seated, probably with a seat belt in an enclosed space. Belt holsters, IWB and OWB can also pose challenges drawing from a seated position. (Practice some defensive drills from your usual spots, drawing with an unloaded gun.)
Shoulder carry can be comfortable, avoids the belt issue, and is generally the easiest to draw from a seated/enclosed position. The only issue for this one is the absolute need to keep on your cover garment. You mention using a second shirt but in my experience, cover garments for shoulder carry should be a bit thicker, stiffer, or otherwise able to break up possible printing. I've done it with a blazer, suit jacket, leather jacket, canvas jacket (field coat), heavy or padded flannel, and even a thick cardigan sweater. You'd just need to try it and see what you need for your body. (I definitely recommend vertical over horizontal for shoulder carry.) Practice carrying over a weekend or something and have your wife, friend, etc. watch for excessive printing.
Generally, I don't like those little single action revolvers in rimfire for self defense. They can work but they present their own challenges and leave a lot to be desired. If none of the other options discussed here sound good, try a high-rise OWB pancake holster for a compact 9mm (or .380 if need be). The side anchor points on that type of holster distribute weight nicely and they keep more of the gun up above the belt line. You'll still need a cover garment but this method could be more forgiving than shoulder carry. Lots of companies make this style of OWB holster but the Galco Fletch is a popular example.
Just be patient and try different things. Having a secondary full-sized firearm in the truck isn't a terrible idea but there are challenges with that too. Having a good firearm on your person should be the main goal. I hope this helps. I look forward to updates.