I totally agree with the idea that if you need to take extra pain relief to do the exercises you shouldn't be doing them. Who knows what's happening to your knee when it's numbed. There's no point in flaring it with too much exercise, I've discovered. One useful PT expert said to me, 'When it hurts, sit down. In fact, try to sit down before it hurts so that you don't trigger the inflammation unnecessarily.'
The NHS prescribes the bridging exercise as part of their phase two programme. They say do it starting with five minutes and gradually increasing. I'm three and a bit weeks post-op and I'm not doing it yet, but I'm older than you are. I have so many jobs to do around the house it's a challenge to do them without flaring my knee.
Just in case this applies to you, I found that the quadriceps-focussed exercises prescribed for me (and everyone else part of the NHS follow-up PT) were unhelpful. What was really useful was waking up my sleeping glutes and learning how to use them properly to walk - which I hadn't been doing for decades.