fritte

Hi everyone. Im very new to this forum but hope you will have some time to help me anyway. Im going to the European Alps this summer for the first time. Particulaly the areas around Chamnonix and Zermatt. I will be climbing in july/august. I would like to know what kind of sleeping bag to bring. I expect to be bivying at around 12000 feet several times during my visit. How cold is it typically at night at this elevation in the Alps? What kind of sleeping bag would you recommend? Thanks in advance