It depends on how much of a project
you're up for. It is all simple work, and straightforward, if you choose to DIY.
We usually go to a foam shop, with the dimensions and have them cut the foam for us. You can use any fabric
you want to cover them. We use a 1/4" piece of closed cell foam that we bond with contact cement to the bottom of the 4" firm foam, this eliminates mildew on the bottom.
When I cover the cushions
, I first pre-shrink the fabric
and drying it. Then I iron it, cut out the top and bottom, then make the strip for around the sides. I prefer to have the zips go from half way up the sides all across the wider part, and half way down the other side, because it is then so very much easier to re-insert the cushion after washing
PM me if you want more information.