You will struggle with both seat weight limits and with Max Take Off Weight (MTOW) in most three-axis microlights unless you can find a jockey to teach you how to fly.
I cant recall the exact numbers (and I'm sure someone will correct me if I get it wrong) but most 3-axis microlights are designed around nominal occupant weights of about 86kg - ie 172kg for both occupants. With you on board there would be only 52kg left for an Instructor - and that's assuming that you are 120kg full clothed!
You will have to look at individual types to see what the maximum seat loads are as they vary from aircraft to aircraft.
Your best place to start would be to lose a significant amount of weight.