It's normal to be scared after having pre-eclampsia.
I decided to try for the second time- after having severe pre-e with my first- because the odds were in my favor. Odds were, I wouldn't get it again since it is more common in first pregnancies. And odds are if you do get pre-e again, it is usually later in gestation or less severe. Of course there are no guarantees though.
I can't say I wasn't nervous trying again- or that I stayed calm during my second pregnancy- but it was reassuring that I was being monitored more closely and more frequently due to my history. I bought a BP monitor to check my pressures at home, and I read up on signs and symptoms of pre-e so I knew what warning signs to look out for.
I'm also on thyroid meds. FYI, last year the American Thyroid Association published updated guidelines for the Diagnosis and Management of Thyroid Disease during Pregnancy and Postpartum
Not sure what guidelines are in UK/NHS but The Endocrine Society published pregnancy guidelines in 2007 (co-sponsored by European Thyroid Association) that also recommend that hypothyroid women get their TSH below 2.50 mIU/L pre-conception
. And they recommend repeat thyroid testing as soon as pregnancy is confirmed. Most (but not all) hypothyroid women need their thyroid dose upped by roughly 30-50% during early pregnancy.
Anyways, I hope this helps, good luck with whatever you decide.