I'm a guy and I have straightened my hair for about 6 years now

What straighteners do you use? GHDs are the only thing that keeps my hair straight all day.

Just make sure you use a good heat protector (not tresemme as it is bad for your hair) and then a serum to protect the hair and keep it straight.

I use Wen cleansing conditioner. I stay away from the harsh chemicals, and sulfates which can damage your hair further, especially if you chemically straighten your hair. Also, using a heat protector is very important as well for when you straighten with a hot tool. Wen has a styling creme in their line that is good for heat protecting. Add back shine with oils!

^ I use something very similar. It was just lying around, and I just thought, "what the heck".? Do you have any recommendations for both Serum and Protector?

Kerstase elixir oil is the best serum you will ever come across. It's not cheap but it lasts forever.

I use this soy and wheat spray! I have wavy/curly hair and it seems to make it dry straighter!