Hi Carol, We sell Sunflex bifold doors, as their looks and engineering are second to none. Their internal SF45 bifolding doors may well suit your needs. There is a choice of thresholds - one choice is a DDA compliant flush track recessed in to the floor sealed with a twin brush pile and a nylon strip for a virtually seamless connection between the divide. You may well want to consider a moveable wall rather than bifolds though, as these can be installed without a threshold. They have a slightly different 'slide and turn' opening mechanism though, but would allow for that lovely seamless flooring. - see the Sunflex SF40-HSW for details You may also be able to reglaze your existing doors - Specialized coatings on the glazing you choose can help provide thermal protection and perhaps save you some some expense. I hope this helps you find what you're looking for. Tom YES Glazing Solutions

Hi. Do you need to access it from the outside? We have done many tilt and turn windows in this type of situation. So you can put it into tilt function for the ventilation needs, but you can open it up fully for access etc. You just can't open from the outside.

Maybe you could speak to them - https://doorwayservices.co.uk/? They do commercial doors so I'm not really sure if it goes with your project

Glazing in general varies hugely in cost. You could get bifolds from as little as £2-3k all the way up to £20-30k. It really depends on what you want to pay for. The budget option is the double glazed uPVC. They are generally quite reliable. The very high end option would be the triple glazed, aluminium frame with "air" sliding. The quality is miles apart but do you really need to be able to open the door with one finger? Does your house have super energy efficiency credentials that will be affected by the budget option? Some are even hurricane tested if you're worried about that. I would recommend a mid range product but definitely with a warranty.