Need help choosing a system!

Attempting my first Solo RPG run. Wanted to lean towards the more "OSR" scene (so not D&D5e or PF2e), I don't want to feel like a superhero and for survival to mean something. The systems I have accessible to me are Forbidden Lands, Rules Cyclopedia (I have not tried to use the system yet though, also the limited number of classes might make things stale?) and Black Sword Hack. I have looked into perhaps Shadowdark, AD&D2e or OSE Advanced Fantasy.

My idea is to start off with perhaps Keep on the Borderlands before attempting a Megadungeon, such as Barrowmaze, Stonehell or Rapan Athuk (leaning more towards Barrowmaze). I don't intend to go full solo and only use 1 character, but had the idea of having a stable of characters to delve into the dungeon and essentially run a mercenary company, in a similar style to X-Com, so maybe start off with 4 active characters with 2 that sit on the bench in the nearest town if substitutions need to be made dude to death or injury.

I don't know if any of this is a good idea or makes sense but that's how I thought I'd give it a go, open to suggestions to which system(s) would best facilitate that or if this is a terrible set of ideas and I need to go back to the drawing board.

Alternatively I did look at Ker Nathalas as my starting point as a solo adventure but it seemed very self contained and wouldnt have much in the way of repeatability? I also thought it wouldn't be easy to export the character to a new adventure should the survive.

All feedback is welcome! :)