I'm happy to describe my experiences with SSRIs, but to be frank, I think I need to address some of what you describe about yourself in your post first. I am not a mental health professional or a healthcare provider, but I deeply empathize with the sense you express that your brain is "all you have."
I also want to tell you that it's a lie. You don't have your brain right now. A well-operating brain does not typically do the things your brain is doing. Maybe by your "brain" you mean your intellect and your insight into your situation, which you fortunately do have - but I can assure you that SSRIs are not going to diminish this, in fact, they're likely to do the opposite.
I take 10mg of citalopram and 60mg of buspirone daily. Eventually, I plan to switch that up and take 20mg of citalopram, dropping the buspirone.* Like you, I was incredibly nervous about starting them. I tried duloxetine (couldn't stomach it, literally) and bupropion (too anxiety-inducing, though it had a nice stimulating effect) before trying my current blend. Each medication brought with it fears along similar lines to yours: sexual side effects, losing my intellect, blunting my emotions, losing my sense of self/continuity. Here's what actually happened:
About a month after I started on citalopram, I encountered a situation which would commonly provoke a panic attack... and it didn't come. I knew that I should feel anxious, that I had felt that way in the past in these situations, and indeed, I was worried - but only in a normal way, "hmm, this could be a problem." Not the shaking and fast breathing and inability to think about anything else that panic attacks bring. It was a fascinating, slightly disassociative sensation, to know that by all the rules of my own brain that I was used to, I ought to be feeling awful, and instead I felt okay. Not happy, not unconcerned, but rational, functional, so, okay. I don't feel artificially happy because I'm still not happy. I'm just able to deal with my problems.
This continues to be my experience. I still have panic attacks sometimes. I'm still an anxious person. But there are lots of situations now where rather than feeling intensely anxious, I now just feel a normal amount of concern. Like a normal person would. I'm still me. I'm as sharp (or dull) as ever. It's just the panic that is missing, and I don't feel any lesser for it.
I have experienced side effects: Buspirone makes me very dizzy, and hungover if I miss a dose, so I take it just before bed. Citalopram makes me more activated/awake, so I take it in the morning. Some people feel the opposite, or nothing. I have had sexual side effects as well. They were moderately unpleasant, but they went away after a few months and now I am normal again. (I'm confident I didn't just get used to them and mistake them for normal, because I no longer have problems I temporarily had.)
Getting on and tapering off these drugs is a pain in the ass. (Start slowly. Do not start with the full 20mg, you won't feel good.) And it is true that there is an extremely small non-zero chance that you could be permanently altered in some way - sexual or otherwise - by trying one. But I would view that as an extraordinarily unlikely occurrence - you are almost certainly not that unlucky, because almost nobody is. I would recommend giving them a try.
A resource I found very helpful was Lorien Psychology's SSRI article: https://lorienpsych.com/2020/10/25/ssris/. This is by Scott Alexander, the same person who writes Slate Star Codex, but is more recent work. There are lots of things Alexander writes and believes that I don't agree with, but he is a licensed psychiatrist and I find his approach helpful.
I also want to say that I think from your description you may need more help than what any med or combination of meds can provide. You should devote the energy you have to finding a good therapist that you can trust. This is much harder than it should be and probably merits its own Ask HN/discussion, but once you have one, you will have a much easier time making these decisions with their help. I recommend regular talk therapy, too - whether with your psychiatrist or a separate provider. SSRIs work best when they are not the only treatment you're trying.
*(Note that buspirone is not an SSRI, which is why I only address it tangentially. I'm getting rid of it because its benefit is pretty marginal compared to citalopram, and I feel disproportionately bad if I miss a dose. It's a great "gateway drug" to SSRIs though, if you want to try it. My side effects are unfortunate but very very rare.)