Edit: Sorry this answer only works for RPi 2. The problem with the RPi 1s is that Debian does not support this architecture by default (ARMv6). So you need to wait for a project or someone to do the build for you.
The following answer only applies to RPi2.
Collabora provides Debian 8 Jessie images for the RPi. They claim it's the official Debian 8 Jessie for armhf architecture but with the Raspberry Pi custom kernel and recompile by them.
The instructions and download links are here: http://sjoerd.luon.net/posts/2015/02/debian-jessie-on-rpi2/
Or check directly Collabora Blog for more recent news if any.