I have thought about framing the inside and having concret delivered to repair the pool but it's a pretty big job for a weekend place. It would probably be costly too. We did use some kind of plastic sheet years ago and fill it up. The plastic eventually started leaking so I removed it. One day, when I have some money I'd like to have it repaired properly. I can afford it right now.
Google EPDM pond liner, or EPDM roof liner, either will likely be cheaper than pouring new concrete to make repairs. Have you measured the old pool?
https://www.justliners.com/epdm.htm
