Thanks for the comments. Jonathan is my favourite so far I think. Sebastian and Nathanial were on my shortlist last time round but vetoed by DH. David is out (close family name) but otherwise sound. William is DS1's middle name.
Agree can't use Henry given the Horrid Henry connotations (didn't even know of Perfect Peter when DS was named which may explain my SIL's raised eyebrows at the time).
I do like Christopher so will add that to the list for discussion with DH.
Rupert is a step too close to Tarquin for my liking... also Rupert, Michael and Marcus fall foul of a self-imposed rule that we would try to avoid using our own initials (to save postal confusion!). Sorry for omitting that from the OP but it had slipped my mind...
Glad Jonathan has a reasonably positive response. Thanks again.
Yep Juliet is on the girls' list. Miranda and Rosamund although lovely fall foul of the "no common initials" rule. Elizabeth is a close family member so no go. I'm rather partial to Jemima (but yet to persuade DH) and possibly Edith (although my family would have a field day with 'Allo 'Allo jokes and bad impressions of Mme Piaf). We do have the girls' name that DS would have had (Annabel Sophie) but I will aim to have another that we both like ready so that as with DS we can decide when we see the baby.