Upholstery and Fabrics - Help, I Haven't Got A Clue

I have an old oak dining chair that I picked up many years ago at a garage sale. At the time I bought it, I removed the seat, fully intending to reupholster it. It's taken me awhile, but I'm ready to do it now.

Problem is, I've lost some parts. All I have is the chair and part of the seat, which looks kind of like a picture frame.

I've cut a piece of plywood in the full shape of the seat and nailed the two pieces together. I then cut more plywood to sit inside the seat "frame", (if I remember correctly, this area was originally filled with straw or something).

I've got a piece of 1 inch foam, but I can feel the wood underneath it. I'm afraid that if I use anything thicker, the seat won't sit right in the chair.

Truth is, it should be a simple job, but I don't know what I'm doing here. My library had nothing specific to what I'm doing.

If in doubt, consult with a professional. Typically, an upholstered seat bottom has a solid piece of wood on which padding and the upholstery is applied to cover and this is attached to the chair frame. A picture frame seat covering may have indicated that the original covering may have been a webbed or woven seat bottom. If so, you can still go with a piece of plywood, padding, and upholstery.

That's exactly what I did. After I cut some plywood for the bottom of my "frame" and more to fill in the middle of it (to make a more or less solid surface, I took my seat to a local fabric store. The upholstery expert there laminated a 1 inch piece of high density foam to my original piece, and cut the whole thing to fit for me.

Anyway, the project is done. I went slowly, put my tacks in only partway (good thing, too, because I had to remove most of them more than once). I had some trouble at the corners, but it looks good. Not perfect and professional, but passable.