Any content which is still protected by copyright ...
... is going to come with DRM. This is simply a reality. Copyright owners have a right to control who publishes their work so they can insure that are being fairly compensated.
Your solution is to get the free Kindle reader App for your tablet (or smartphone) and the corresponding free apps for your other content. This will reduce you dependence on devices down to the device of your choice, Mac/PC, tablet, or smartphone.