If you have a symptomatic tear, and the surgeon thinks a trim will help, then presumably he or she will trim.
Ref a TKR, unlikely you'd get one on the NHS but you could get a private opinion (10-15k probably. Normally TKR is indicated if there's bone on bone arthritis in more than one compartment with severe impact on activities of daily living and all conservative methods (physio, injections, pain medication) no longer helping. Not sure what you mean by a lower chance of success? In a TKR, they remove and replace the worn out ends of the bones. If only one compartment, an osteotomy or partial replacement could be considered in younger patients.
If you have a TKR young, you'll likely need a revision if not two down the line, which are more complex.
Based on what you say about your symptoms, a TKR should be far down the road for you

a partial menisectomy might provide the relief needed if a tear is the cause