Evening concert, what to wear?

[AuroraBunsenBurner]

It's been so long since I went to a concert that I am somewhat out of touch. I am a bit of a homebody to be honest. Although fond of clothes I haven't had to dress for a night out in so long I have no idea what's what anymore. I like subtle, simple things, nothing flashy or frilly or busily patterned. Any advice?
Anything I really shouldn't wear? That might help!
I like the idea of loose velvet trousers and a plain silk jersey top, but it might be OTT? I don't have any 'going out' type shoes either, just chunky boots! What footwear would even go with smart-casual trousers? My Docs won't work with slinky trousers..

if it helps I am 46, longish wavy dark blond hair, small boobs, average height and weight.

This will be the BBC Philharmonic.

Depends where they’re performing!

If it’s the BBC Studios at Media City then wear what you’d wear to M&S to pick up some groceries.

If the Bridgewater Hall in Manchester - your proposed outfit would be fine, but take your grocery shopping coat. And a scarf.

Any further afield - maybe take a smarter coat.

Unrelated to concert-going - its awfully annoying to have great trousers and no footwear to complement them. For ‘absolutely not dressing up’ velvet trousers, these might be grounding:

https://www.grenson.com/nina-womens-loafers-in-burgundy-hi-shine-leather/

I've been to 100s of classical concerts, venues in UK and Europe and big name orchestras. People don't dress up for classical orchestral concerts unless it's something like the Viennese New Year's Gala concert. It's everyday, what they were already wearing clothes. Your outfit would be a bit OTT.

Thank you, this is good news! I did a bit of research and it does appear to be more casual nowadays, but for some reason I can't bring myself to wear my lace up docs.
I do have some flat black chelsea boots though, so all isn't lost.

DP says he will be wearing khaki chinos and a tshirt with converse. I think it's that my everyday style is very outdoorsy, wax jacket and jumper, etc, so would prefer something maybe a bit more sleek, personally, although don't want to over do it.

Your Chelsea boots will be fine, as would the Docs.

I wouldn't wear the wax jacket just because lots of concert halls don't offer cloakroom facilities and there often isn't much space to cram a jacket that doesn't fold up well under your seat. I'd put crush-up-ability and don't care if it's shoved under a seat over style so far as the jacket but with something you feel nice under it like your plain silk jersey top.

Enjoy the concert.

I will try to simplify, thank you!