When I want more loft and quilting definition I will often layer up two different battings. My favorite combo for doing this is Hobbs 80/20 on the bottom and Hobbs Polydown on the top. It gives wonderful definition but the quilting requirements are 4" apart minimum for those batts. This is not an issue for me usually as I am a fairly dense quiltier anyway. Wool also offers definition and loft.
I have used Mountain Mist Fatt Batt in the past for tied quilts. that is a very high loft poly. I haven't used it in a long time though. It appears to still be available in precut sizes. I would not buy a whole roll of a fatt batt. I will double bat for the high loft trapunto look or do traditional trapunto.