Sounds like you got the NOW Freeview Smart box with the blue NOW TV name on the top box casing if it doesn't support the Disney + App anymore.
Unfortunately NOW don't sell either the NOW boxes or NOW Stick anymore where they have been discontinued.
Look at something like a Roku player or Amazon Fire Stick has a replacement, though these devices don't have a Freeview inbuilt tuner with a TV aerial connection on them and you will have to use alternative means to watch Freeview (unless you keep watching on the NOW Freeview Smart box).
On Amazon maybe (surprise, surprise!) but if you cast your net wider, to Currys or Argos for instance, you can get a Roku Express for what Roku say the RRP is:-