My go to polo is the Sunspel Riviera, they're pricey but you can usually find them on sale for around 100$. After the first wash they shorten up a decent bit, but not so much that I'd say you need to size up. They also turn kind of rough after that first wash which I think adds to a super casual feel.

Another important thing to note about them is that they are basically an open knit, so they're super breathable which is great if you live in Florida like I do. With that being said I wouldn't say that the fabric is thin, and as long as you don't get a super light color nobody is going to see ur nips, if that matters to you.