Our caves here are colder than yours, but drier. We often wear both thin polypropylene underwear and a furry suit under our oversuits. I have found tho that two-piece combos are better than full furry suits so that the jacket and/or pants can be deleted if you think you're going to have a warm trip. Pile or fleece jackets are also widely available at regular or discount clothes shops and you can pick them up cheap off-season - get the full zip version rather than the pullover so you can unzip to cool off. Stuffing a balaclava, toque ("wooly hat") or neck-gaiter into your tacklebag can help with those waits at pitches if you've underdressed.