I use a DD superlight hammock. It's on the short side at 2.7m (just shy of 9ft) which works for me but I'm not that tall (170cm) but might not work for you. Most people aim for 11'-12' hammocks, and I've heard of people going up to 13' and 14', though I think those people are 6'6+.
I don't really see why any hammock would be more/less comfortable for the length as long as you hang it correctly. Are you sure you're hanging it correctly? It should sag down a lot more than most people expect so that you can lie in it diagonally. Pic related>$24
Hammocks are literally just a rectangle of fabric (hence why comfort should be pretty consistent). You can buy 4 yards of 1.9oz ripstop from RSBTR for $13, and turn it into a hammock with a sewing machine and an hour of your time. Just sew the long ends over, and then sew cord channels at either end. Hammocks are mostly all around the same width at 54"-56" and that's because fabric is sold with 58" widths, and then you lose an inch or so on either side when you sew the edges over. >>2024246
Underquilts are relatively new. When I got into hammocks about 8 years ago it was quite difficult to find quilts at all. They definitely existed, but not as much as today. It's still mostly the realm of cottage companies and the few companies who do made good underquilts now can charge a lot because supply isn't that high.