I think you may be right, does it feel spongy when you walk on it? If de-thatching is required you can hire a vertimower or pay a contractor to do it for you. I don't have any experience with it myself so you'd have to make some enquiries. It may be worth coring (aerating) also. If you know of any contractors that provide free quotes it wouldn't hurt to ask them their opinion on what's required and how much to do the vertimowing. Definitely do the PH test still as the soil could be contributing to the issues just as much as the thatch.
