Welcome 🙂 120cm is about 4ft in old money so quite long to be fair, by “mobility chair” do you mean something line the Maclaren Major or a typical wheelchair just smaller for a child? Only asking as we’ve just returned a Vauxhall Astra and my wife’s wheelchair fitted with ease but a friends Maclaren Major was to long and had to go in diagonally or leaning upwards.
Our new car is Seat Leon ST and whilst the boot is slightly smaller the wife’s wheelchair fits fine but again the Maclaren Major wont.
Can recommend both the Astra and the Leon – currently an auto Astra starts at £499 for the Elite Nav (top spec) and the Leon ST at £0 with £99AP getting the top spec version. Our Astra was the Elite Nav and whislt not as sporty as the Leon was comfy, well equipped and very practical – only had the Leon for a few days but first impressions are really good.
EDIT
Pretty sure the 12months is when you place the order, not at the time of delivery. Also if it helps with dimensions of boots, door widths etc https://www.ridc.org.uk/content/car-search has quite a few models listed with lots of info.