Classic Navy White Gingham. This is a casual shirt so I went with a light weight fabric. I also have a dress shirt made of Grandi & Rubinelli Navy Gingham Oxford, a mini gingham that is seriously nice.
I'm not a fan of 3-piece suits so mixing it up takes a little of the stuffiness / bankerness out of it. I'm not keen on wearing the jacket and vest with different trousers, but swapping out the other 2 pieces can work. Obviously wearing matching jacket and trousers with a lightweight sweater in place of the vest is a classic look. Wearing the matching vest and trousers with something like a heavy shawl cardigan in place of the jacket can be next level brilliant (or it can...
The collar is the same material as the shirt, navy knit pique. Specifications were:
7" pullover placket with 3 buttons.
Collar: 1.75" back height and 3.5" point length.
Soft collar but with a stiff neckband.
Note: this was the linen-cotton blend, which shrank like a mo-fo in the wash. The material feels fantastic, though, very luxurious. If you opt for this either keep it away from warm water or account for shrinkage in your measurements.
Polos/rugbys are traditionally knits. Here's my favourite polo collar from Luxire, which has a medium back height, long collar points, and (here's the key) I asked them to make a stiff collarband but leave the rest of the collar soft. As far as I know nobody else is doing this and it makes a big difference: the collar holds up even if you want to wear it under a jacket, but the points still drape softly and comfortably.