Help me find a summer dress for bbq

[BoysRule]

I just don't know where to look. It's an informal celebration bbq but more dress informal than shorts and vest informal.

I am size 10, 5ft 6", broad shouldered so I find shift dresses and high necks make me look wider. I like just above the knee. My fave shops are Jigsaw, Reiss, Mint Velvet, but I'm just not seeing anything I like. I hate sales too so I think that's not helping as it's all sales. I need to be careful with fabric colour under the arms too as I do tend to sweat!

Any ideas of where else I can look?

what is your hair and skin and eyes colour?
are you floral or plain and monochrome?
how old? (roughly..)

I'm late (very late) 30s. Blonde (fake) and fair skinned. I'm happy to floral but like a sophisticated, sleek look. I've got my eye on some tan Jigsaw sandals to wear (flat).