I agree with finding someone to do a good evalutation.
DS is on meds, but a very low dose, especially considering his size. I didn't want to med him either. It finally just got bad enough during the school day that we tried the meds. As a child gets older, in about 3rd grade or so, the school day requires more sit-down concentration.
It might take a while to find the right med at the right dose, and your dr should want to be in the middle of that whole process and taking input from you.
As far as diet goes, there are several things I avoid, and I did buy the Feingold kit for reference. Everything as "natural" as possible and unprocessed. The artificial food coloring is evil stuff (especially the red), as is MSG and preservatives. However, that's a big committment too. Unless you typically cook all his meals from scratch... and don't eat out often... and the best way to approach it is if the whole family eats that way, which is certainly healthier but you can meet with some resistance. If you child is old enough to appreciate a Happy Meal or Pizza Hut, you're gonna have a fun time taking them over to Feingold. It's one thing if you start them out that way as a toddler, and one thing if they're old enough to really understand what you're doing (like in their teens), but it's very hard from my experience to switch out foods on a child that's elementary-aged and all they see is that they aren't getting McDonald's and the good cereal anymore. Since also at that age, they don't have a full understanding of ADHD, they don't understand the need to "fix" it. So the first thing you'd need to do is talk to your child and explain the diet stuff to them in a way that they understand and get them on board with you. Even if you monitor their food and their teacher knows too, there will be times when the "bad" food is presented and they need to understand what to do and why.
Okay, that was a very long and confusing paragraph.
If you really want to go diet, going to a DAN dr is probably your best bet. Not for the diagnosis! But for a treatment plan and further testing. But they're
expensive.