Downdraft extractors are not as efficient as those above as they extract the air below most saucepans. Have you thought about something ceiling mounted?

Hi The Bora was the big purchase for me. I have the simple model. I have it on the island and have a vaulted ceiling above it which meant that a ceiling extractor would not work. I love the Bora, the fan extraction is very effective if a shade noisier than I had hoped but very much quieter than my old extraction hood. The house is free from cooking smells and there is less grease to be cleaned from tops of walI cabinets etc. It is simple to use and as the extractor fan is operated from the same set of buttons as the hob it goes on sooner and more often. I got the system that ducts outside (the piping is invisible, under the kitchen floor). The hob top extractor fan filter goes straight in the dishwasher - the whole hob is easy clean. It was installed by my own kitchen fitter with no problems. Beware the ducting pipes are extra and not cheap.

A lot of appliance dealers online show the specifications and although the slide up extractor may be slim they also have a motor underneath which would need space which you won’t have because of the oven. I think your options are to make the worktop deeper, move the oven or to have an overhead extractor. If you are simply looking to avoid an old fashioned looking chimney extractor there are other options.

We worked closely with a high end bespoke maker early on in our kitchen remodel saga.... they weren’t keen on downdraft models because of how much space they take up underneath, not just the unit itself but the venting. I suspect that might be part of why the builder doesn’t recommend it, as it will complicate fitting.