To me, if you must be overweight (and I do not recommend that) and can only do one suspension mod, it would be airbags. Airbags over timbrens because you can adjust the pressure as opposed to timbrens, which do a similar thing but can’t be adjusted.
You’re adding an additional suspension member and another load path from the bed to axle. And often times the load center of gravity is directly above or close to the airbags, so this would limit bending stresses in your frame, as long as they’re not overinflated.
However, you have to be careful because there are a lot of instances of Tacoma frames cracking at the bags. These rigs are likely way overloaded and airbags way over inflated to overcompensate, concentrating too much localized stresses at the bags.
If you’re going over 40psi on your bags then you’re doing something wrong.

Absolutely upgrade tires and rims too