Those are both good methods listed above.
One more that you can add that will work both extensors and flexors of the forearm. Fill a bucket with white rice so that you can put your entire hand in it. Move your hand and fingers around as much as possible for 30 seconds and then switch. The rice supplies the resistance against movement to strengthen the muscles.
These methods are all good for developing forearm strength but if it is an issue with the structure in and around the wrist you might need to consider wearing some form of wrist wrap when you train the lifts heavy. That's the only real way to protect the bones that make up the the wrist. You should note that training heavy should also develop greater structure strength in the wrists, but I am aware of many people that just don't have the joint thickness to support heavy weights and need wraps.
I would try a couple of months training your forearms for better strength and then also look into the wrist wraps right now. If you develop enough forearm strength you might be able to wean yourself off of the wraps over time, but you will just have to play that by ear.
Scott Edson
Credentials - Masters in Exercise Science, Former Division I Strength and Conditioning Coach, owned a gym in Chicago, Currently operate my a fitness website -