Insulation

[loves2read]

passive roof vents really work better than a power/electric/solar vent fan because which tend to draw air out of the cooled spaces in the home into the attice via gaps in electric/plumbing runs...
make sure you get ventilators with the widest throats---they generate more air flow/movement than the more narrow (and cheaper) units and made a genuine difference in cooling capacity

you need to check the soffit vents--if they are not open and functioning so that outside air comes into the attic/over the insulation that is down--then any ventilation effect is cut really down...

many homes new and old have soffit vents that are not really opened because the wood fascia around the opening is not cleared away--
you might also have something blocking the vents

I know that some people say radiant barriers are not effective but go into two homes -- one with and one without the roof decking with radiant barrier--and you will notice a difference in the attic temps

the spray on barrier must be done right (too much spray is not cost effective and too little is not temp effective) to make worth the money and it is less effective than the decking
the foil that can be added to the attic ceiling needs to have an air space between it and the roof decking to be most effective--many companies won't take the time to install it correctly
and the foil that is added to the attic floor can become covered with dust/dirt over time which reduces its cooling ability
you need to get info from good company about your specific situation
not all houses --based on orientation to the sun/trees/venting/roof line--will benefit the same and it all depends on how long you anticipate being in the house for a payback curve...
for most people there are other energy saving/heating/cooling tips that can help you control costs with less expense...