Sorbothane record weight?

Hey Mike, check out my system https://systems.audiogon.com/systems/8367 Check out the turntable. Check out the clamp. DIY clamp btw. DIY clamping system. Look real close at the platter. See that little black washer around the spindle? Its just thick enough to hold the center of the record very slightly higher than the platter. The clamp is dished out. So when the clamp is tightened it pushes the record down onto the platter outer edge first.

Even somewhat warped records lay completely flat. The record is so tight and secure on the platter that when I get done with a side and remove the clamp the record sometimes sticks a second or two and then pops up. Why? Clearly the atmospheric pressure was holding it down. Yeah. I know. Miller built a freaking vacuum hold down without the freaking vacuum. Pretty amazing. Even for me.

A few record weight i've been using long time ago are on this image. 
The one on my SP-10mkII is a German Made for 30 Euro, the grey one on the left side designed not only for LP, but also for 45s (also nice and cheap). They are lightweight under 300g each. 

If you want the original look for Orsonic clamp that you can lock to your spindle. 

That Orosonic the collet style and will work on a smooth spindle.

Both Mitchell and Record Doctor make very simple and successful record clamps that really do push down and help flatten the edge.
Nothing new really however that's not really what the OP was asking.
But I have found that the Mitchell clamp requires more of a spindle standing proud of the album than the Record Doctor one does so at just $29.95 from Audio Advisor it might be worth a trial.
Also handily happens to weigh 350g....

Thanks for all of the input.  Unfortunately, It’s not as simple as buying a weight or clamp.  My spindle has a pop up plastic collar around it that drops down when an album is on the platter, leaving only the metal center of spindle above the label.  It is less than half the diameter of a normal spindle, and very short.  Without a record on the platter to hold the collar down, the platter will not turn.  (Cartridge safety feature). The platter and tone arm assembly are suspended from the underside of the plinth by three springs, now 30 something years old, and the recessed platter surface is only barely above flush with the plinth.  A 200 gram LP plus 300 grams and the platter IS flush (I checked) with the plinth as the springs stretch, and the very outer edge of of the album can make contact with the plinth.  That’s why I was looking for and trying to find something light other than the clamps I see to damp vibrations on the vinyl.  I’ll try the sorbothane and let you know if it makes any noticeable difference.  I’m using a SoundSmith SMMC 1 cartridge.

Steve