I think the one in the link will take you down to 50-55dF although that is a nice price.
You should be able to hit 16-18 +- oz with climasheild quilt good to 40dF depending on the size.
I am a side sleeper too, and have been testing a quilt I built about 4 months ago. Slept in it a lot. Originally it had a drawstring footbox, but after playing around with it a bit, I have modified the design into something that works better for me. IMO a drawstring closes the end down too much vs extra length needed vs weight, so I changed it to just a velcroed flap, IE the last 12" and the footbox is velcroed together into what would be a vertical seam.
Being velcro, you can open it completely up, add a triangle footbox end or whatever, but I did find as a side sleeper the vert velcroed end fit my feet better than a drawstring setup. Oyu could also do it with a zipper if you dont like velcro.
On the real deal I will be making shortly out of climasheild, I will build in a baffle to go over the end.
Should cost about $120 in materials. Mine should end up about 14-15 oz.
I am trying to set it up as more of a system this time, IE the quilt will fasten to the bivy top, the bivy wide enough for a neoair large inside the bivy. The quilt closes down to the edge of the neoair etc.
As a side sleeper, if I am in a mummy bag I turn the entire bag so the face hole says in the right place.
With a quilt I turn over under the quilt.
Here is a plan of the quilt I have so far, but I need to take a few more measurements. Its based on the one I have now. I am tall so its long. It is almost exactly 3 square yards, so in my case with 1 oz momentum you would have 6 oz of cloth + 3 SY of 2.5 oz climasheild or 7.5oz + 1oz velcro, drawstring, straps and misc = 14.5oz
Oh yeah, get a neoair. Its comfortable and very light.