Wedding guest dress help

[LaLaPlanned]

I need help to find a dress for a wedding I have coming up next spring. This is a close family member’s wedding and I would like quite a formal but comfortable option. My preferences are:

1. Has to be long
2. Has to have sleeves (at least half sleeves)
3. I will not be wearing heels, so needs to suit ballet flats
4. Would prefer that it is not very flowery or patterned
5. Needs to be formal/evening wear
6. Budget up to £200

About me:

I am late 30s, hourglass figure, size 18. I have darker features and suit bright winter/dark colours. I have a larger stomach, so prefer flowing fabrics (chiffon etc.), and am 5ft6.

Even just an idea of which brands to look at would be great, I am struggling with the usual options (Coast, Roman etc.)

Any help greatly appreciated!

Karen Millen
Goddiva
Monsoon (occasional gem)
Phase Eight

I have this from Next in a different colour and it looks far more elegant and expensive on especially when teamed with nice earrings, bag and shoes.
Also good underwear!

I got a dress virtually the same as this from Debenhams around a hundred quid. Very flattering indeed and I find myself wishing for other occasions to wear it

Thanks for these suggestions, I like the dresses in Phase Eight and Goddiva, and like pleated/chiffon styles. I can’t do satin but that dress is beautiful @SkinnyOatFlatWhiteForMePleaseBarista