@Lemlems this is a great opportunity to pay attention and find out what you like, then 😊
It's only in the last few years that I've started to pay more attention to the feel of things, myself. I'd been overly logical and 'practical' in the past, without taking into consideration my other, less-logical responses to physical materials.
Noticing more about my own response to materials makes a surprising difference to my personal levels of contentment.
Maybe try a selection of small amounts of different fibres, constructions, etc, discover how you feel about each one, and then explore more in that direction??
My (adult) kid likes fluffy soft novelty fibres (like the kind you might use to knit a baby blanket), and can't usually tolerate hand-knitted items in animal fibres (such as any kind of wool, no matter how soft). Something about the ridges of the knitting touching their skin, I think.
I'd suggest starting with yarns that the retailers say are good for baby garments, because they're usually soft and they *should* be machine-washable (if they're not machine-washable, they're not really suitable for babies, because parents of small babies do *not* have time to handwash).
In Australia, this is my default baby-friendly yarn: https://www.bendigowoollenmills.com.au/luxury-8-ply
(I don't buy much yarn from retailers outside Australia, because shipping is too expensive.)
If you are willing to say what area of the world you're in, you may get some more specific brand recommendations
Ravelry.com is handy for looking up what other knitters have to say about any yarn you're considering. Sometimes people will write their opinions of a yarn in their project notes. I don't know if you can see this page without a Ravelry login, but here's a bunch of projects knitted with bendigo luxury 8ply https://www.ravelry.com/yarns/library/bendigo-woollen-mills-luxury-8-ply/projects