If you are on the hunt for the perfect Christmas gift, give a Kindle. I'd recommend the Kindle Paperwhite as opposed to the earlier Kindles that look dull by comparison – not to mention, its power consumption is miniscule. Then direct the gift recipient to the Project Gutenberg, where more than 40,000 classic books are available for Kindle (and other formats) for free.
The device is seriously optimised for fatigue-free reading. Even regular iPad or Surface users who think they can read long tomes on those devices should give up on the idea and get a Kindle. Since Amazon developed the touchscreen you can casually plough through a book holding the device with one hand and tapping the screen to turn the page.
Amazon created the Kindle to exploit the market for eBooks, which it sells by the boatload. And if you like popular modern fiction, Amazon will be your primary source. Amazon's cloud will maintain your library so if your Kindle gets upgraded or crushed, you can easily reload your library. You can back up eBooks you download from Gutenberg via a USB cable on your own computer.
There are other sources of free material including google.com/books and archive.org, a treasure trove of scanned books. I'd recommend checking Gutenberg first if there is a specific book you want on Kindle. Gutenberg books are edited after scanning whereas text from Google Books and archive.org are essentially raw scans. This is fine if you want to look at the raw scanned page, but they are run through an OCR program to produce a MOBI file for the Kindle. The OCR used is probably state-of-the-art but that still means it's lousy. It's impossible to get through anything without hundreds of annoying typos and screwball errors.
Amazon also has many older books available for cheap on Kindle and often promotes new books at bargain basement prices, so there is plenty to choose from.
The last book I read was the classic and influential The Coming Race by Baron Edward Bulwer Lytton. Although written in 1871, it's easy to read and is an early example of Victorian era science fiction, although it was never referenced as such at the time. This and other old books actually seem more readable on the Kindle than in print.
For example, my son read the works of PG Wodehouse on his Kindle. I have never thought much of Wodehouse although many writers adore his material. When I began to read him on the Kindle I realised his work flows in ways it never did in print.
That's because an e-reader is an entirely different medium and it works better with certain styles of writing. I'm not sure if this has anything to do with the restricted fonts or what, but something is different. Old texts perform very well on the Kindle and things you found unreadable in print might be great on the Kindle. And if you run into unfamiliar words, simply place your finger on the word in question and a dictionary opens with a definition.
I have played with the more tablet-like Kindle Fire and like the device for its versatility, but for a pure reading experience, you can't beat the Kindle.