I wish there were a way to disable the sensor short of mechanical contrivance (such as a software setting). The vest pocket I often put my kindle in is close in proximity to my phone and magnetic pocket closures, so it tends to wake up spontaneously, as I only recently discovered. I have also been carrying it in there with my Kindle Touch (which has a cover) which also triggers the sensor if they are 'face to face''. No wonder the battery drain has seemed excessive.
I tried a third party cover and like other commenters here, found it did not reliably keep my PW from waking, as even slight movements could trigger wake. I would like to think that the Amazon cover would not have this issue, but then I like using it without a cover and do not want to spend $40 just to solve this spontaneous wake problem.
I will probably experiment with affixing a thin magnet to the bezel where the sensor resides to see if that has the desired effect.