My OH was in the same position kneewise. He didn’t want to be on endless painkillers, doctor useless etc etc. We read lots and tried lots and now he has gone from being really crippled a year ago to pretty supple in his knees, walking much better and for a lot longer. Our solutions have been cherry active a supplement from H & B. If you google cherries and knee pain etc you will find articles on it. I got some as I expected it to be another expensive failure but it was a pretty instant success. It also helps sleeping. Cost is £30 a month. Got to be the right cherry supplement not a cheap one from Tesco.
Secondly, when he really really could hardly move I got him a pedal exerciser. That is pedals that you sit on a chair and pedal. Cheap ones are around £20. To start with about a minute was a struggle. His knees were really painful and locked up. Fast forward a year to now and he has the real thing ie a bike and we do 20 mile rides. The key for that was strengthening the muscles supporting the knees. He went along with all this as he was really unhappy at things like knee operations, replacements etc or drugs and ibuprofen was the thing that worked best but not at the amount he was taking. but he was becoming very stuck in his knees otherwise.