We got mine from the Diamond Store online - https://www.thediamondstore.co.uk/
We found them to have a good selection and not be too expensive for what I wanted. To be honest, I chose a few rings in different styles that I liked and let my fiancé choose which he wanted to get for me. I had an existing silver ring which stood as my 'placeholder' ring for a while, but my friend got engaged and then chose her ring afterwards as well.
As for what to look for... I'd probably say the usual - guarantee, reviews etc. Is it a surprise proposal, or can you take your OH along to see what they like? It's sometimes nice to choose together - at least I thought it was!
My fiancé knew I loved gold over white gold just from my usual jewellery choices and he picked the ring, I felt like it was more special that he put thought into it and chose it. When my sister got engaged, her fiancé had put a placeholder in so they could choose together. It’s completely down to you and what you think she’d like
So I popped into a shop today and took one of her rings with me.
I said my budget was £1600 to £2500 (basing this on Google saying the average is £1800?) Anyway I described a ring i liked and she brought one out but it was nearly £3900. I liked the ring but couldn’t tell if I was being hard sold. It seemed like a lot of money.
We bought mine after we got engaged and went into shops to narrow down styles I liked and confirm my size. We then looked online separately for a few days and then came together to share our favourites and there was a ring from the Diamond Store that we had both picked so went with that one.
Unless you know exactly what kind of ring she wants, maybe waiting until afterwards to pick together might be good. £3,900 is a lot of money for a ring, does she wear expensive jewellery at the moment because I would feel really nervous wearing something so expensive. I also wouldn't buy from a shop that completely disregards your budget and shows you something twice the price.
Unless you are planning on buying a super cheap ring, either propose without a ring, propose with a placeholder or ask her what she wants first. I've heard loads of horror stories of women who were given rings costing thousands which they absolutely hated but felt they had to wear because their OH hadn't bought one that could be returned/swapped!