EDIT: Success, thanks everyone!
EDIT2: I forgot to backup the kernel image for 5.2.0 -- does it actually change during the update from 5.2.0 -> 5.3.0? If not, that's no problem, it would just be nice to have it. If someone actually did backup the 5.2.0 kernel and it differs from the 5.3.0 I would be very thankful if you could provide me with links here or via PM!
EDIT3: Nevermind, ixtab has it covered
EDIT4: I just compared the md5sum from my "mmcblk0p1.bin" with ixtab's "pw_5.2.0-mmcblk0p1.img" -- shouldn't the md5sums match? (because they don't). I also have a Kindle Paperwhite WLAN 5.2.0 image.