You live in a mild climate area, hot summers 90 degrees, cool winters.
I presume the amount of insulation is OK for the winter?
It's the summer you are concerned about?
The big problem is the amount of heat gained by radiation and the effect of conduction through the wood frame of your home?
Filling the attic with insulation will make a difference.
However, the radient heat landing on the roof, will enter the attic and you need to deal with this by fitting sheets of polystyrene covered with a reflector to bounce this heat back into the sky.
Dealing with the conducted heat is more expensive.
The best solution is a new SIPS roof with a covering that is either silver or white.
To keep your home as cool as possible all walls that are heated by the sun sould be covered with SIPS, where the polystyrene inner is at least five inches thick, preferably eight inches.