platter mats for dd turntable?

The current stock rubber mat for SL1200s isn't as good as the old one was, which was 1/4" thick and weighed over a pound. You can still buy this mat from http://www.kabusa.com. It's called the Technics Supermat, and is about $20. Herbie's Way Excellent also offers a wide range of mats at reasonable prices. If you go Herbie's, pick a mat of the same thickness as your original; with an SL12x0 series, pick the one closest to 1/4" to get the right VTA range.

Others have spoken highly of the Iron Audio mat.

I use a sorbothane (but not sorbothane gel) Oracle Groove Isolator mat on my SL1210 M5G, but they're long out of production. I have been very pleased with it. Definitely lowered the noise floor and cleared up murkiness in the midrange and brought out inner detail and clarity.

If I were starting fresh I'd probably get a Herbie's.

I have a Herbie's on my Technics SP-15 and like it much better than the 1/4 inch one pound Technics rubber mat from my 1200 or the 1/8 half pound Technics rubber mat that's standard with the SP-15. Lowers the noise floor considerably, I'm guessing because it's more forgiving of minor warps. The Technics rubber mats are pretty hard.

As Johnnyb53 says, get the right thickness for your VTA range which, depending on your cartridge and arm, may or may not be 1/4 inch. Also, the Herbie's comes in different diameters, so make sure you get the right one for the 1200. My SP-15 takes a slightly smaller one than the 1200, and I was lucky to find one used.

David

It's worth bearing in mind that the Technics 1200's platter has a slightly raised lip all the way around the edge. Some companies are starting to notice and provide slightly smaller mats that fit inside this lip. I've had best results with a SoundDeadSteel Isoplatmat (285mm to fit the 1200) directly on the platter to damp any ringing and a Funk Acromat on top to interface with the record. This combination only lowered the noise floor a touch, but it did things with air and space that I hadn't heard from a Technics before.

I wouldn't worry too much about matching the original mat's thickness - the Technics' VTA adjuster is very flexible and has quite a wide range.