I am so sorry about your little boy. Most of us either turn out to have no underlying conditions at all, or something that's often pretty minor (and common in women with totally normal pregnancies too); there are no real answers here and that is so hard to accept when you've lost a baby, and something I still struggle with 15 months on (believe me, it will get easier though).
I am now 16 weeks pregnant again and very scared but hoping for the best. Statistically, most women who get PE have it worse in a first pregnancy and I try to hang on to that (though its hard to predict for any individual woman and baby). I am taking low dose aspirin (for which there is some evidence of a small benefit); calcium supplements and high dose folic acid (for which there is no evidence that they really help much, but they don't seem to do any hard either so I'm trying them).
I can't say its been easy to get this far, but I would suggest you speak to a high risk specialist who may well have a different opinion about your case, given that they are more used to handling similar cases compared with a regular OB.
Even though my PE was life-threateningly severe I was never discouraged from trying again; quite the opposite really. My docs are confident they can manage my care if I get sick again; just no guarantees for the baby.
I hope this helps a bit; take care