Hey hun u could look into getting an open return they cost a little more but if ur not taking a Virgin train on the way back it should be cheaper. Prob best to stay in London until 12- 24hrs post op like others had suggested in case of complications that you can’t sort out whilst in transit.
Plus u may want to avoid rush hour time due to crowding and pushing. If u can book a seat that would really help and avoid a scrum! Fxx