Hi Julio
If the options are those 2 sleeping bags, then your cousin should take the 30/40F one. Job done.
Why?
- even unheated albergues will average many degrees warmer inside than the outside temperature (and I'm not sure there are any unheated ones open all year anyway)
- nearly all albergues provide blankets
- as you point out, with the thicker one he’ll boil when he gets to a warm place like the Xunta albergues in Galicia (cheap and open all year) where some of them still don’t regulate the temperature well and the radiators are on much of the time.
- the chances of the only option being an unheated albergue without blankets in frozen conditions are very very small. And in that case he'll have the adventure of coping by putting on all the layers of winter clothing he has packed ;-)
Now that you and he have decided on the
Camino Frances life is going to be a lot easier. I'm very glad to hear that!
FWIW I've walked it in December in snow blizzards over the mountains and in temperatures well below zero and with a wide range of folk (old, young, pregnant, with donkeys etc) some of whom only packed summer sleep bags - and it all worked out fine.
If you are still concerned about the availability of warm and reasonably priced accommodation, you can always check on the
Gronze website. You or your cousin can pick out some likely destination towns, check for albergues open all year and look at their facilities and ratings. You can likely do this on apps as well, such as Buen Camino and
Wise Pilgrim.
Cheers, tom