Think about the ages each of you children will be when you potentially decide to become a surrogate. How will your energy level be with say a 3 1/2 year old and a 1 year old at home or a 4 year old and a rambunctious toddler? Will you be able to devote the kind of time and attention to your children while being in the 1st, 2nd or 3rd trimester of a surrogate pregnancy. How will it be if you are potty training one and your youngest isn't sleeping well AND you are pregnant? How will you feel if you are in pain while nursing or lose your milk supply? What if your pregnancy isn't quite as easy the third time around? Are you ready for the changes a third pregnancy can have on your body?
I think its great that you are considering helping another family have a child. That is a wonderful gift. Make sure that your family and you are taken care of first. I agree with the PP that your body needs at least 2 years to recover, if not more. I would wait until both children were potty trained and maybe one was in preschool before considering it. After I had my son I had a strong desire to be pregnant again or pregnant still, I think those are natural feelings, but I would focus my energy on the newest addition to my family and put looking into surrogacy on hold for a while (at least 6-9 mo). You may feel different in 6 months, if you don't, look into it a bit, call around see what you can find out, ask your. Dr., your husband.