Don't go to high street chains.
My gf designed the ring herself. We bought the diamond on its own for 77 Diamonds and went to an independent jeweller for the band and designed it with the person who made it. I guess you could do all that in secret, or buy the diamond and let her design it? Luckily my gf isn't very traditional like that and I knew she would prefer to design it etc.
The whole thing was literally half the price of the high street, twice the quality and you get aftercare on both forever.
I had no idea how much of a rip off the high street was. They just prey on men not having a clue.
That was over 5 years ago, still not even close to getting married lol