You would have access to any lounge (keep hold of your F boarding card to show for this), but would have to go landside for the arrivals lounge. The three lounges in the south end of T5 (CCR, Flounge & Galleries Club) all share the same showers, whilst the North Galleries club has a few of its own. Breakfast is available in all lounges, but will be limited to a bacon sandwich in the Galleries Club lounges - the Flounge and Arrivals will have a buffet style English breakfast, whilst the CCR (or CCR dining room within Arrivals) will have the same via table service. No need to book anything.