Don't focus too much on the 'hat' remark.
It was more to make the point that if you're not fully attaching a system as you eventually intend it would be, perching a system on your head was never going to be a good representation of what it is truly like to wear a system.
Therefore, why bother to do a trial run with a system, you might as well use a hat.

But I will say that in my opinion, the quality & quantity of hair you have left is not worth you being so precious over.
The majority of the area has hair that is so fine & sparse, you don't even need to bother shaving it. You could glue/tape over it and still get a decent bond.

The hair at the front is slightly thicker and you could try getting a very light density system and sit the front of it behind your natural hair and blend it all together.
Then, if you ever wanted to go for a higher density, you could decide to shave off the front and cover the entire area with a system.

But in truth, I think you're more emotionally attached to the hair you have left than the reality warrants.
That said, looking at what style you achieve with concealers, the result (in photos) is remarkably good!
But I promise you that dumping the concealers and committing to a system will be a day you remember as the best thing you ever did.
No more mess, no more hours in front of the mirror and so many more styling choices.

One of your concerns is about gluing your entire head and the thought that the scalp can't breath.
At this stage, that concern is just a thought and without shaving your head, it will always remain just a thought.
Thats what I mean about not really being able to gauge what wearing will be truly like by compromising the experience.
You're not giving yourself the right opportunity to address your concerns.

I recently switched from a lace system to an ultra thin skin system and I had all sorts of preconceptions about what it would be like. It turned out that none of them were founded and it was other things that I hadn't even considered that were more relevant.
One of my concerns was that the scalp wouldn't be able to breath.
Don't ask me why, because I still don't understand it, but its actually not a problem at all.
After 18-20 years of wearing lace base replacement hair, I thought I'd have a pretty good idea and was 90% certain I wouldn't like wearing a skin system. I was completely wrong.

So this is why I feel you'll never really know until you try, but that 'try' has to involve giving it your best shot.
The best way to do it is to commit to the idea of wearing and go for it properly and make it work for you.
At the start, the likelihood is that you'll encounter a few issues and you really need that determination the push you through the difficult early learning stages and persevere.

All my hair fell out in one weekend and the subsequent transplants left me with no option but to cover my head with a system.
Looking back, I'm kind of grateful it happened that way because I HAD to make it work.
I think if I'd had an alternative, I might have given up and that would have been a big mistake.

I wish you all good luck in whatever you decide to do.