I ordered four of my usual bra one in each of the sizes suggested. Having just had a trying on session I am not convinced any of them are right but I can see now that the 32C I am wearing is not right either. My usual bra is the Wonderbra t-shirt bra as I like my underwear not to show under my clothes and they provide good 'nipple coverage' being moulded. This could possibly be the problem as I think I read somewhere that because moulded cups don't fit to you it's hard to get a good fit?
Anyway, here's the feedback:
The standard Wonderbra t-shirt bra doesn't come in a 30 band so I had to order the 'D-G' version. This is far too 'over engineered' for the smaller band sizes, with a really thick band and straps. I'm used to a more 'delicate' appearance!
The 30 band is very tight on the loosest hooks and gives me 'back fat' overspill that looks most unattractive under a t-shirt. I am a size 8 and don't have much fat round my ribs so this is quite an achievement. Also, was digging into my sternum.
DD cup is too big - looks OK till you discover that I'm not filling it despite scooping. E cup is huge!
The 32 band fits fine on the loosest hooks but, the 32C I am wearing is now on the tightest hooks and possibly a bit loose so I'm not sure whether I do need the 30 band after all. 
32D - again the band and straps seem a bit thick and the cups, though providing a much better fit over my boobs, were digging into my armpits. Not sure if it's just that this is how it's meant to be and I'm just not used to it. Did still have the not filling the cup problem but not as much as the DD cup.
32DD actually felt better in the armpit area but had the same problem with filling it that I had with the 30DD - felt like I was putting on a pair of false boobs!
I'm guessing that I need to try a different style.
There seems to be a big difference between the 32C and 32D - I feel like I'm in between those sizes in this style.
Any further advice? Thanks