as far as I know, there is no option to choose a "singles only" mode at the beginning of a new career. Of course noone is forced to play doubles tournaments, but in order to develop a strong player over the years I need the experience points gained by playing doubles. So, in every tournament I start in singles and doubles, having no fun in doubles at all, because I'm no great fan of tennis doubles and in my opinion, in TE, doubles are not as great simulated as singles are.
I think it shouldn't be too complicated to give the choice "Singles only" at the beginning of a career, with the result of being unabled to sign for doubles all over the career and gaining a larger number of experience points for each singles match (I think it should be raised by about 50% compared with the normal singles+doubles career). Would you try this?