If you want to be extra secure you could use a VPN before Tor. But using a VPN would make you suspicious as well. They could force the VPN provider to track your future connections over their VPN. I assume it's not that easy to trace your connections if your using tor.

Best is to install Tails on a USB Stick, boot it on a public computer over public WiFi while being completely covered with no mobile devices on yourself. But let's be serious. The given thread model involved in downloading a book, the risk of drawing the attention of the authorities is probably very low. :)