A Clark's 3, Breslow 0.7 mm is not too advanced a melanoma - depending on where it is - can you see it easily without a mirror? Is it in an easily accessible place for palpating it? Every three months after a wide excision is pretty standard, but if you are anxious about that part of the follow-up, by all means, ask for a second opinion. It will set your mind at ease, and it should not be any offense to your surgeon.
Good luck to you - and I'll be keeping you in my prayers.