Hello, just wanted to post an update on my decision.
We went to the jeweler yesterday (yes- a month after we were supposed to

) and I tried on various plain shanks as this was the look I was going for. The jeweler also presented me with wedding bands and allowed me to try those on with my ER and with the plain shank ERs that she was showing me. My FI did not like the look of a plain shank with an eternity diamond WB, and especially not with pave diamonds on the WB (which is the kind of WB that I would like). He prefers a plain shank with a plain WB. When I tried on the stackable pave WBs with my current ER they fit perfectly together and looked beautiful. Both he and I agreed on this.
I decided to keep my current setting, and suggested that in some years we should revisit getting an upgrade and a reset... DF agreed =)
Thank you all very much for your advice and suggestions!