You definitely want to get two guidebooks by William O. Sullivan: "100 Hikes in the Central Oregon Cascades" and "100 Hikes/Travel Guide: Eastern Oregon." Bend is pretty much the boundary line between the two, so you'll find mountain hikes in the first and high desert hikes in the second. While these are in dayhike form, many are backpackable. I'm also limited by physical issues to 5-7 mile days, so I use Sullivan's books as much for backpacks as for dayhikes. I'm sure they are available in local book or outdoor shops; if not, there's always amazon.com.
Your part of Oregon is especially attractive to us "wet-siders" at this time of year. For early trips (like this month), the Metolius River Trail is a popular choice. You can also drive north to the mouth of the Deschutes River and backpack upstream. Plus there are lots of fascinating places in the high desert (found in the Eastern Oregon book).
Hopefully Jerry (retiredjerry) will come in here; he's been to that area more than I have. Also, you might want to browse the trip reports on www.portlandhikers.org for those from your area.