I don't have the same car as you but the mirror I bought has the straps you can pull taught in both directions, so I'm assuming you could just use the ones that wrap around it horizontally? By the time I'd done it up horizontally I couldn't do the vertical ones up anyway! I'll get a link...
https://www.amazon.co.uk/gp/aw/d/B08CDL7W69?psc=1&ref=ppx_pop_mob_b_asin_title
I have the same car and couldn’t find a mirror so I got a camera one from Amazon! So I can watch my son from the drivers seat on a camera monitor thing xx
I have the same car and have this mirror. Put it on the middle seat head rest and angle it round to see little one 😊 https://www.smythstoys.com/uk/en-gb/baby/car-seats-and-bases/car-seat-accessories-and-toys/babylo-baby-rear-view-mirror/p/204931
I have a Mercedes CLA & I struggled with this too. I bought the dream baby one which is one that straps underneath which we obviously can’t do, so I’ve just had to leave that undone and strap it around the headrest. It’s not the most ideal but it works for us, we just have to be careful knocking it x