I would personally always go with a waistcoat the same colour as my suit.

You can only go wrong with a navy suit if its not tailored correctly! Personally, unless you’re looking to draw attention though I would avoid any bold colours with the waist coat and tie.
If i was going I would just keep it simple. Well tailored tweed sports coat with a deep navy knit jumper and pale shirt underneath. Moleskin trousers in a dark brown or navy. With brown leather penny loafers or twin monk shoes.