What to wear to a big birthday party at a bar?

[TripleTruffle]

I don't go out at all, I'm mid 30s and a size 12/14 at the moment. Any suggestions welcome as I'm in a panic now about what to wear.

My go to is usually a blazer and body with jeans or wide leg trousers and a nice top but that feels a bit too casual. I do like skirts and dresses as well, just don't know what to go for, for this special occasion.

Wear your comfortable dancing shoes and clothes.
Beautiful hair and makeup and a smile on your face would work.
Feel confident in yourself xx

Are your wide leg trousars black? I'd wear black trousars and a top, either black or something with black in it like an animal print.
Blazer or long tunic vest over top.

Whose birthday?
What type of bar?
What are your general preferences?
Budget?

Whose birthday? - Best friend
What type of bar? - Relatively upmarket with a dancefloor and garden.
What are your general preferences? - A dress maybe? Something long sleeved as I'm expecting it'll be cold in the evening in the bar's garden and don't necessarily want to be taking a jacket/blazer on and off all night and carrying it around.
Budget? - £80 (I've got blazers, trousers, shoes and bags I could potentially and match already)

On a budget of around £80 (some of these go to £100) for a long sleeved party dress my go to would be Sister Jane.

https://sisterjane.com/products/blues-jacquard-midi-dress

https://sisterjane.com/products/gilda-jacquard-maxi-dress

https://sisterjane.com/products/showstopper-jacquard-maxi-dress

https://sisterjane.com/products/feature-bloom-midi-dress

https://sisterjane.com/products/fantasy-jacquard-mini-dress-1