Vacation homes and apartments in the Kander valley
You'd best consider a home or apartment in Frutigen if you prefer a town with restaurants, shops and good public transport services. Kandersteg is a bit smaller, and closer to the highest peaks. Spiez is even larger than Frutigen, and more lively. It's on the northern edge of the valley. Traveling times into the valley are limited though.
Interhome offers thousands of holiday homes and apartments across Switzerland. They offer discounts on both early and last minute bookings. That makes the Interhome website a good place to start your search:
https://www.interhome.com/switzerland/: all holiday homes
https://www.interhome.com/switzerland/early-booking-discount/: find the discounts for early bookings
https://www.interhome.com/switzerland/last-minute/: find the last minute offers