Thanks for all the replies.
I went for the Yellow (we'll be lovingly calling it our 'banana boat') 2 person Kayak. Will let you know how it goes. If we both end up enjoying it I could see us getting one of the more advanced options in the future.
Appreciate all the warnings regarding safety, especially at sea. I grew up visiting my Gran on the south coast where my Dad had various small yachts and his skipper's license. Lots of pottering around the Solent, couple of flotilla holidays etc. So I've probably had more experience at sea than the average person. Definitely know to respect the water and not take any chances! Having said that - It's probably quite unlikely we take 'Banana Boat' out to sea, not until we've been on rivers / lakes a few times and got a feel for it.