Hi everyone, I'm new here.

Question... I am suddenly having a tough time with threads. For about 10 years I used an older White sewing machine, which worked fine with pretty much any thread I would put in it. I mostly used Coats and Clark (thats what my Mom had always used), and it worked great in my machine.
Well that machine finally kicked it, and I upgraded to a Janome MC 6500. I LOVE the machine, but I am having a tough time finding threads that will work well in it. The Coats and Clark does not (which, upon researching online, I found this thread definitely isn't considered to be that great), the top thread looks great, but the bobbin thread underneath is all loose and wavy. Gutermann does okay, but still not 100% - still some looseness with the bobbin thread (yes I've checked all my tensions).
When I bought my machine, the dealer gave me set of Iris Ultra cotton quilting thread. I finally tried this the other night and WOW! The thread feels sooooo good in my machine, and the stitches look beautiful! I was all set to go online and buy a huge set of all cotton thread... but then it hit me that cotton thread may shrink in the wash. Is this correct??
I sew a lot of handmade clothing and accessories and sell them on Etsy. I do prewash all of my fabrics to avoid shrinkage after sewing, but you can't prewash thread. Should I steer clear of cotton thread for this reason? If so, what polyester thread should I try next??
TIA for any suggestions. I really want to get to sewing with this new machine, but want to make sure my stitches look good enough to sell. Thanks!!
