What do I wear for dinner in London?

[WatermelonSugarSigh]

I'm going on a work dinner soon to a cafe/restaurant in Clerkenwell. Looks a really nice place- live classical music performances etc.

I have no idea what to wear. I don't want to look overdressed but at the same time it looks nice and I also don't want to be underdressed. Im early 30s, 5ft5, size 10, slightly pear shaped. I wear dresses a lot, mostly midi/maxi, don't like above knee. Probably going to wear flat tan sandals. Like boho style a lot. I'd like to buy a new dress but no idea what to go for. I also don't want anything polyester but viscose is fine. Can't really spend more than £100.

Any ideas will be gratefully received 😁

Literally anything goes in clerkenwell but casual is better generally. If you want to wear a dress I'd say midi rather than maxi. Sandals will be fine though I cannot get in board with the socks too that everyone wore at Colombia Road the other week! Cover up with anything though big jumper rather than coat.