I bought most of my thread from ThreadArt - it's the same thread as a bunch of others, just packaged under different names.
Their set of 160 different colors is on sale for $190, this week, which seems like a really great deal to me - there is a LOT of thread on these mini king cones. This was the most economical way I could find to get really good quality polyester embroidery thread in a large range of colors all at once. And the thread is shiny, smooth, embroiders beautifully either computerized or free-hand and I've never had a problem with a single spool I've bought from them.
I use them as quilting threads and painting threads, too.
They also sell bobbin thread in 60 wt in very large cones - only black or white. I think the diameter is similar to Bottom Line, which is 70 wt. Either of those work well on the back of embroidery.
I buy their pre-wound Style A bobbins when they're on sale - 144 bobbins to a case and they last a LONNNNG time. I can use these in any of my machines that take a class 15 bobbin. This is very fine thread - it might be the 90 wt you're looking for. It's practically invisible on the backside except for the sheen.
I stayed away from rayon because it burns too easily and can change color in laundering. The polyester is colorfast and you can iron it if you don't use the high setting on your iron.
http://www.threadart.com/c-2-thread.aspx