I think that this is a really hard decision, but one DH and I have just gone through. We have done one stim cycle - 5 x embies, 3 x BFN, 2x did not thaw. For a number of reasons, for our seconde stim cycle we decided to put two fresh back - partly because we lost 50% in thaw so we wanted to minimise the number frozed, but I think we will also put 2 frozen back as well. While it wont double the chance, it will give you an increased chance of falling pg - but also of having twins - which does have down sides. Be prepared though for how you will feel if you put two back and get a BFN - as I think we are about to, as it is really hard to deal with esp if you only have low numbers of embies in reserve!

Good luck
FG