Sometimes the best solution is to do nothing. The more we worry about the problem the more it affects us. Sometimes a good short haircut can make the hair appear thicker and fuller.
When David Beckham shaved his head and made it fashionable suddenly thousands of men breathed a sigh of relief, shaved their heads and stopped worrying and started enjoying themselvs again. So maybe doing nothing at all is the best solution but having all the available information can only help you come to the best solution for you.
Avoid using hair products like gels which stick hairs together as that can make the hair appear thinner. A good wash every day can make the hair look thicker......