Looks like you’re going for a classical guitar version of a baritone guitar, which are electric steel strings, have a longer scale length and are usually tuned a 4th or sometimes a 5th lower than a regular guitar.
It seems like you can take a regular set of strings but offset them by 1 position so the 2nd string would be where the 1st goes, etc. They would be tuned about a step lower than they normally would, A instead of B, E instead of G, C instead of D, etc. so maybe a high tension set might work better.
The problem is finding a string to serve as your low A. Maybe from a Mexican Guitarrón or Bajo Sexto? I’m not sure if the latter uses nylon or steel strings. The other issue is because of the short scale length the lowest string might not have a very good sound.
Like you mentioned, I would also be concerned about stressing the instrument so if you have a less expensive guitar you wouldn’t mind experimenting with that would be the way to go.