Breathable waders and splash jacket with layers underneath. I haven't used it yet, but the
mysterioso stuff looks like a good base layer.
Peeing can be difficult, but it's not impossible. The warmth all morning is worth the inconvenience in my opinion. I've used splash pants or a wetsuit before, but the waders were a huge improvement in comfort and warmth.
I would highly recommend against the rain slicker (button up jacket for walking in the rain, correct?). Go with the splash jacket.