Yo! I will tell you what I did. I found a standard ring. Nothing fancy. Just a solitaire (ring with one rock on the top). The key part was that I went with a company that allowed trade ups. Meaning that I could return the ring for full price after the purchase as long as I was using the money to buy a more expensive ring. So I did that. Bought the normal standard ring, did the proposal, then went to get a new ring by trading it in so my partner could get one they absolutely loved.
IMO lab grown vs real diamonds are a non issue. They all look and act the same aside from having a laser etch.
For gold silver platinum, up to you. Again, you can always go standard and trade up (as long as the company does that).