Lady Emma - at your height (5,6 if I remember) I think the 30cm would look good you, perhaps in a softer leather and a lighter colour, so it appears larger, a sheenier leather would appear larger too. It might do for when you want to bridge the gap between day and night without changing bags and need something a little more smart-casual rather than casual. I've agonised for weeks over the 30cm vs 35 cm size and although I have a 35 cm Kelly, I am going to go for the 30 cm Birkin and use it as a hangbag not a tote or travel bag. A small enough laptop would fit easily, not sure about shoes though. I quite liked the 30cm having less depth than the 35 cm, that swung it for me more than anything else, I think there's about an inch less depth in the 30cm Birkin, so it should be more streamlined than the 35cm and less likely to bump into things and a softer leather would benefit from fewer bumps.
Meant to add, have you considered a Bolide in 31cm? That way, you could stay faithful to your 35s and have a smaller bag with a completely different look.
Thank you for the thought - I DO like the bolide...but the larger sizes!

I am going to go poke around and see what's there. I may be best served in the the midsize kelly range 32. Thanks!