The doors you are referring to are called pocket sliders. They are very expensive around 180 a pair, although as they're meant for joinery, the cabinet maker would need to fix a 16-18mm jamb and create a recess for them to slide back into, this would effect the opening access of your doorway. I don't think these are the best or easiest solution, however they could be adapted to your needs. Personally, I think the FOC Face of wall sliding door is the best solution, given you have at-least 900mm on either side of the door to accommodate the open door?..if you don't; then, without knowing your house style these may be way off, how about bar doors, the name escapes me the ones in western movies where they're either side and you push through them. I've see them in a solid core door, so at-least they close themselves, and you could teach your cat to nudge through them, so its tidy when they're shut.

I think sliding door takes up less room, I just put one in my laundry/bathroom. We brought the frame and sliders as a kit from masters and purchased door separately just their cheap internal door, as the door hangs from runners it is not quite touching the floor I don't think their will be any water issues

Either one serves it's purpose for different situations. I sometimes prefer stacking sliders because when they are closed (which is most of the time), they have wider glass panels, so form nicer windows. But bi-folds give you a wider opening when actually open - eg. 100% open rather than just 2/3 open. Stacking sliders can usually have sliding flyscreens as well which is sometimes a preference depending on which part of the country you're in if you want to keep insects & flies out!

Hi again, thanks everyone for your input. I have been to a well known window/door manufacturer today which makes aluminium, timber and alu/timber composite to compare all options. It was a local company also so they were able to advise based on knowledge of our climate. The composite was higher in price but was also too contemporary in design, the aluminium was also too contemporary in design and not all options suitable for double-glazed glass, so we have returned to the idea of the solid timber but have taken all the advice on board and are opting for a pair of hinged french doors with sidelights in size to match and fanlights above so we can still retain the overall height and look but the actual doors will be closer to standard 2100mm height. Hopefully this will also eliminate any difficulty with opening them which we would probably have found had we had a bi-fold system or 2.7m door height. FYI the salesperson I spoke with also advised that there is a product available (sold in our local area from Inspirations Paint company) which when applied to the timber doors/windows gives 7 year protection from rot and fading due to rain and UV. He had used this himself on his own timber doors which were also exposed fully to the weather and highly recommended it - so I will post what this treatment is when I have more information on it. Thanks again everyone who helped out with their advice