I've never heard of a Sew Slip, but if it is like the Free Motion Slider or Supreme Slider, it is a teflon sheet. I have a teflon sheet I purchased some years ago from a sign supply shop to use as a heat press cloth. It works just as well today as it did then, & the surface is still just as slick. I would suggest looking for something like this (google search) if you do not want to pay that much, although, you will have to put your own hole in it, and use double sided or even carpet tape to hold it down. I bought a can of Quilt Glide from my local quilt shop for $8.95, which works great. You spray it on your table tops, quilt bed, and anywhere else you want to reduce friction or drag on your quilt and wipe/buff it off. It is super easy to use, works like a charm (it reminds you of putting
Armor-All on leather seats- slippery), and lasts through at least 1 king size quilt. (I am speaking from experience) The website listed on the can is:
www.jukeboxquilts.com
Hope this helps.