Guys, you might not have noticed, but the OP lives in Birmingham, UK not Birmingham, Alabama. So references to US stores might not be very useful once you factor in international delivery charges and times
I did wonder about an air mattress or blow-up chair, but thought that by the time you've faffed about finding where the pump got to and pumping it up (and then finding the cat has sharpened it's claws on it), and clearing the lawn/patio of anything that might puncture it, the sun has gone in and it's started raining. Far simpler to have a bean bag to pick up and plump down where you want.