My initial thoughts are to head direct for Santa Fe New Mexico and then pick-up Interstate 40 thru Flagstaff AZ.
I came back to Cedar Rapids IA from the west coast along an essentially similar route in 2013. Generally speaking it was Mojave to Vegas to Albuquerque, and then back (we took a northern route on the way out over Rapid City, Salt Lake City, Lake Tahoe, etc). I was a pretty low-time VFR-only pilot at the time, and it was my first "real" cross-country trip (we had an absolute blast!). It was also my first time over any kind of real terrain... that had me quite anxious to say the least!
We were in an Archer and never had to go above 11,500 on that route (eastbound), with personal minimums of 2,000' AGL clearance at all times. I think you can pretty easily do it at 10,500 westbound, certainly 12,500. I wouldn't say O2 is worth the effort for this trip unless you really want to take a more direct route over the bumps. That wasn't even an option in our lowly Archer
In my opinion, as a flatland pilot it's worth the relatively few extra miles to dodge the worst of the terrain and stay near an interstate when the land becomes more unforgiving and remote. There were parts of central AZ and NM where flight following lost us on radar (and radio!) for sometimes 50 miles at a stretch. It's nice to have a paved interstate with cars on it in sight during those times...
Other general tips I'm sure you already know or have already heard, but I remember learning and using on our trip:
-Try to avoid winds aloft >20kts to avoid mountain wave or turbulence when near the mountains.
-Maintain >2000' AGL at all times.
-Sometimes it took a 1-2 day delay to achieve the above points while maintaining VFR. Part of the fun of flying... overnights in random towns!!
-Watch out for restricted airspace! There is a LOT out there. Flight following can save your bacon on this, but don't rely on it. Sometimes if they are cold they can vector you through or above.
-(IMHO) Pay the extra money for full-serve fuel... the FBO's have tons of free advice and crew cars etc. Really helpful if unfamiliar.
-Pack and dress for the terrain you're flying over, not the weather at the destination.
-Bring snacks, water, a handheld radio and PLB (I have
this one)
Most of all, have fun!!! It's a total blast and huge reward to start descending into California with the terrain behind you and the Pacific Ocean in sight ahead