Adrian - it really depends on what you need in your next car. If you want another SUV, I would suggest the NX. Excellent customer satisfaction / reliability ratings year after year. I think a similar size to the RH, and a little smaller and cheaper than the RX. Just make sure you ensure whichever vehicle you go for has the balance of the 10 year Lexus warranty on it, is not affected by the Canbus issue (or if so has had the steel plate and/or GPS tracker fitted). If it's older than 2018 it probably won't have built-in Apple Carplay or Android Auto (AA). So either pick a newer car, or you can retro-fit a new gizmo to add carplay/AA (I did this to my 2016 300h).
So many options including 300 vs 350 vs 450. Hybrid vs plug in hybrid. I think the 350h may be the sweet-spot now (especially with better fuel economy), but you can buy a used 300h for less money.
Looking at the Lexus used car stock, you can pick up a reasonable 2018-2020 NX300h for somewhere between £20k to £30k depending on age, trim level and mileage. The newer 350h starts at about £34k.
Happy hunting!