Like I said, wow! Didn't expect such a response, I've tried to join a couple of other sites to get this kind of advice and not really got anywhere before. Thank you all so much for your kind words of encouragement! It is nice to hear from both SOs and CDs - I appreciate it a lot.
It's no big deal but just to let you know that we're not married - happily living in sin! To be honest, my partner's ex-wife was never told about about his 'secret', so I feel very privileged that he felt he could share with me - this tells me more about our relationship than a thousand words could?
Anyway, I'm slowing building up to 'the night'. We went into town today and I took my partner round some shops and (as well as asking him what he thought of clothes for me) I slipped in the occasional "See anything you fancy?" and commented on a couple of shoe shops that do larger sizes. I think he was quite pleased.
The only worry I think I have now (believe me I have been through the whole range of emotions and paranoid worries that I gather most SOs have, but I think these are in the past now) is that I know he has a variety of clothes (I asked him about his tastes, etc) and I'm not too keen on the sound of his 'clubbing' gear? I don't want to offend him, and I know this is just my personal taste, but I'm worried it sounds a little tacky?

I like to glam it up for nights out and I'm known for being a little daring but I don't think I'm ready to see the club wear on my partner. Some of you may think this is mean but if one of my girlfriend's were to ask me what I thought of an outfit I would be honest and I know they would be honest with me too. Anyway, I guess I'll cross that bridge...
I'll keep you posted with goings on - and thanks again to all that replied!