There is a reason that both sizes exist. The exact setup is an individual choice for every person. Just like deciding on if you prefer a large or a small phone, or a large or a small laptop. The choice is personal.
My solution was to have two iPads. My main 'workhorse' iPad is the 12.9" because it's just so much nicer to have the larger canvas when doing anything from writing notes, to doing emails, editing Podcasts, viewing media etc. But... it's just too big for me to use comfortably as a bedtime reader. I tried for a few months and then gave up.
I would think that any of the cheap iPads are great for this, but I really notice ProMotion on the iPad and iPhone (but not so much on my desktop weirdly) so I browsed Craigslist and FB Marketplace for a discounted 11" iPad and picked one up when I found a good deal. I use it mostly as a bedtime reader, but it's also become my travel iPad because the 12" is a bit clumsy to travel with.