If you want a tablet then the Nexus 7 (2013) is the one to go for. Jack of all trades, fast, great screen the best small tablet out there. You have the advantage of being able to look at multimedia which you can’t do on a dedicated e-reader.
If you go for an e-reader then look no further than the Kindle Paperwhite. Small, light screen readable in all light conditions. You can read it in bright sunlight or when your partner is asleep. You can’t easily read tablets in sunlight so they are not much good outside. You can change text size and fonts, etc. I only read books on a KP as it’s comfortable to hold in one hand and I can use it outside.
My preference would be for the KP if you do a lot of reading. There is an updated KP coming out in October which you can pre-order so I would wait for that.
Both Waitrose and John Lewis have these on display so you could try them out and they all give a two year guarantee which is worth considering. Over to you….