We use this in our model X and 3. Works equally well in both:

TFY Universal Car Headrest Mount... https://www.amazon.com/dp/B01H3DRTIM?ref=ppx_pop_mob_ap_share

We also use this on long trips. My 10-year-old who has a ton of little tchotchke crap loves it.

Backseat Car Organizer with 12"... https://www.amazon.com/dp/B097XX8GZ4?ref=ppx_pop_mob_ap_share