My son was a baby when I went through a divorce. He wasn't quite two years old yet. My ex said he wanted 50/50 custody, but he wanted it on paper for child support reasons.
My son went with his dad on Tuesday nights and Thursday nights and every other weekend. There were times my ex husband was out of town and I had him more. There were some times when I had to go out of town for work and he stayed with his dad. It was that way for many years.
My son is now 17 and he stays with me during the week because I live closer to his school. He spends most, but not all, weekends with his dad. At this age, he pretty much goes back and forth however he wants and his dad and I are fine with it.
You're in California. So am I. At least in my county, unless your ex agrees to your proposal, your child will likely have a schedule very similar to what my son had.
As a mom, yes....I often felt like the poor kid was going back and forth too much, but he loved his dad. His dad did things differently than me. Not better, not worse. Just different.
In the long run, my son has turned out to be an amazing person who loves both of his parents and fortunately, has taken the best of each of us and is more than okay. He's awesome.
For the sake of your child, as a child of divorce myself, please don't think of your son as a "poor little boy" being thrown back and forth.
Divorce is ugly and painful, but children can be okay if their parents are okay and they have the consistent love of both parents.
It will be harder on you than on your son, but you have to be strong and willing to compromise. You don't want the court making that decision for you whether you like it or not.
I wish you the very best, and for what it's worth, often they will reschedule a mediation appointment after 6 months or so to see how things are going. Sometimes things do need to be adjusted a bit here and there.
It's a process.
Again, best wishes.