Dress for work event - help!

[tubaplayer]

I haven't really been clothes shopping since having my DC 4 years ago but I'm presenting at a conference next week and need a smart dress. I feel utterly clueless! I will need to shop online and don't really know where to start. I briefly looked at Hobbs and Whistles but they were so expensive. My budget is around £90.
I'm 5'4, size 10 - 12, skinny hips but busty so high necks don't suit me. I usually buy dresses just above the knee. Can anyone help?

What about something like this or this, from Phase Eight?

Navy v-neck

Wrap dress to go under a jacket

Will you be wearing a lapel mic when you're presenting? In which case you'll need something at the waist it can attach to

V neck (maybe not smart enough? Depends on audience)

Something from ASOS
THIS type of thing
Wrap dress with a nice cardigan
Too bright??

I wouldn't go sleeveless unless it is under a jacket or bolero.

Mega smart would be a woven shift dress with sleeves.

Sorry, I attached the wrong photo to the link above. It was supposed to be this one. I agree about the sleeves.

Thanks so much everyone for your suggestions, I really appreciate it. I'm going to sit down now with a cup of tea to look through them all.

All great suggestions, thanks again. Think I like the M and S one best, burnishedsilver. I usually go to work in jeans so am getting pretty excited about wearing a dress