Welcome to the forum. Plenty of good info in the archives if you want to spend some time searching.
Some of the most frequent advice is some variation of:
1) Seek out the very best Cardiologist and Surgeon that you can. I am guessing that Stanford is a great place to start. There is not much, if anything, that the top notch people have not seen and they have a game plan for any surprises.
2) Focusing on attitude and emotions is very, very important.
3) Having a postop caregiver and comfortable facilities (e.g. adjustable bed or recliner, no need to climb stairs for a while, easy access to the bathroom, etc.) lined up really helps with those first few weeks after the procedure.
4) The odds are usually very much in our favor as the success rate is very high unless there are compelling complications. Being elderly does not necessarily hurt our chances.
5) A successful valve replacement is an extended lease on life and is terrific when compared to the alternative.
Best wishes for a successful surgery and a complete and rapid recovery.
HTH