Light weight long sleeve cotton sweater

The "fine gauge" cotton sweaters from LandsEnd are not bulky. All cotton sweaters tend to be heavy, IME.
I like the 4-way cardigan from Nic and Zoe. Here it's in a lightweight cotton-modal blend from Nordstrom Rack:
https://www.nordstromrack.com/s/nic-and-zoe-all-year-4-way-convertible-cardigan/7498722?origin=keywordsearch-personalizedsort&breadcrumb=Home%2FAll+Results&color=4444444EKX
I also have it in a linen blend.

Look at LL Bean.

You might consider this cotton modal from Uniqlo

https://www.uniqlo.com/us/en/products/E465484-000/00

Or this cotton one from Loft (I’m earring one now)

https://www.loft.com/clothing/cardigans/cat1330002/modern-crew-neck-cardigan/778831.html

Thanks so much for the recommendations, will definitely check them out! Yes, cotton does seem to be thicker than what I’ve seen in wool but I do prefer as natural a fiber as possible.

You might look at Quince... great prices and quality!

Look for Comfort Colors long sleeve tees. 100% cotton. The fabric is heavier. They also make crew-neck sweatshirts and 1/4 zip sweatshirts.

Eileen Fisher is having an end of season sale atm. They have lots of linen, linen/cotton blend sweaters and cardigans. Not budget, but the sale helps.

I don’t know if you’ve considered this but as someone allergic to wool, my go-to if I want both warmth and lightweight is a fleece. I have quite the selection of thin fleece sweaters (half-zip) in attractive colours and they have the advantage of drying almost instantly if you need to wash it.

Golden Girl, is there a particular brand you like for thin fleece? All my fleece is too heavy and like the OP, I prefer light weight layers that aren't bulky.

LL Bean has some lightweight fleece.
https://www.llbean.com/llb/shop/127499?page=womens-soft-brushed-fleece-full-zip-womens-regular&feat=feather%20fleece-SR0&csp=a&attrValue_0=459&searchTerm=feather%20fleece&pos=1

I can't wear wool sweaters, and usually opt for fleece, but a fine-gauge cotton sweater from JJill has been really useful and packs even smaller. The one I bought isn't current, but they might have something else that suits.

Golden Girl, is there a particular brand you like for thin fleece? All my fleece is too heavy and like the OP, I prefer light weight layers that aren't bulky.

I’m in the UK so I get them from a shop called Mountain Warehouss, which does really lightweight thin ones for virtually no money.

I don’t know if there’s an equivalent in the US.

I have these in a lot of colours.

Thanks everyone for the great responses! I looked at one of the pullover sweaters I own that is finer gauge and can work as a little 'dressier' sweater for dinner and daytime, and it is a mix of cotton and rayon. The rayon might be what makes it a finer weave so something else I can look at for others.

I agree with Sharyn…check Quince…very, very nice quality and such good prices!

Just another thought - November in Northern Italy, I would want a down jacket with a waterproof rain coat over it. I have a very lightweight, packable down jacket from Costco, (similar to what you'd find at Uniqlo).

Think my request might have been a bit vague, this is for a finer gauge sweater to wear underneath. We are starting in the Veneto in mid-Oct, ending in Ljubljana/leaving Nov 3. I definitely plan to bring a down jacket and also waterproof jacket as outerwear.

Chiming in a little late, but I would also recommend checking out Boden's offerings. They have several styles of light weight cotton sweaters, often in a wide variety of colors. I used to wear them all the time when I worked in an office. Not the cheapest, but they'll last forever. They also offer cashmere, but if that's all you see at first, keep scrolling the cheaper, cotton ones are there too!

debbied, my LLBean summer catalog came yesterday and I saw this sweater on the back. It’s a Pima cotton cardigan, and looks very lightweight. Hope you find what you’re looking for!

https://www.llbean.com/llb/shop/504209?itemId=527340&attrValue_0=Raven%20Blue&sku=1000327098&pla1=0&qs=3159622&gclsrc=aw.ds&gad_source=1&gad_campaignid=20657335810&gbraid=0AAAAADoqq1IEiZK75WOJ0hKXmNvzn10ww&gclid=CjwKCAjwpefSBhBvEiwAzyEtZ5-VA_laWm-3RvPqPivgMWXnUczkQD1a99y_SrIRQ_-NlYsw5nYEWxoCmEkQAvD_BwE&originalProduct=5840712

I have this one from JCrew Factory. It comes in multiple colors.

https://factory.jcrew.com/m/womens/categories/clothing/sweaters/cardigans/classic-cotton-cardigan-sweater/MF162?display=standard&fit=Classic&color_name=white&colorProductCode=E5957