Looking for yarn for a mobius scarf

I would like to make a mobius scarf for my sister-in-law for Christmas. She is VERY picky when it comes to fibers…she will only wear cotton or silk. I’m having trouble finding a nice yarn. I would like a varigated color and the pattern has a lace design, so it needs to be a fairly smooth yarn (not nubby). Any suggestions would be appreciated. Thanks

I just bought some Patons Silk Bamboo for a shawl. I haven’t started it yet, but it feels very soft.