Thinking of adding a 25th word to my seed

I’m looking into the idea of adding a 25th word to my seed to help with security. Overall my main concern is how will I access this wallet if ledger was to go out of business. I’m familiar with how to recover my funds using the standard 24 words but not sure what happens when you add the 25th.

Could somebody eli5 the risk of adding an extra word to my seed in the event of needing to recover on another device?