I've used Autocraft seat covers a couple times -- they are made by Lebarron-Bonney. All fit good. If using for replacement upholstery and removing the original you will need a thin foam or quilting padding (1/4") to go over the original foam for a tight fit (instructions say so!). I used one without the original covering for a bottom cushion on a Rambler bench seat. I had to get some similar color vinyl and lay under the cover around the reclining seat hinges because the stitched "notch" for the hinge was a bit generous, but other than that I had no complaints with any of them.
The little Ramblers typically had grey seat covers in all the base model cars because it went well with any interior color. A dark grey may be your best bet.