In my experience, the biggest problem will be finding liners, bags, or even quilts with full separating zippers that run down the side and bottom. Opening these zips allows you to use the bags as open blankets/quilts, instead of as a bag.
Without zippers, you end up in a form-fitting silk or synthetic bag that you cannot easily get in or out of. As a 70 - ish fellow, night time bathroom needs must be considered. Not having a zipper along one side is a non-starter for me.
I have a microfiber, rectangular liner from Alps Mountaineering that fits the bill very well. It works well for late Spring, Summer and early Autumn Caminos. But it is not warm enough for winter sleeping in an albergue.
I also have it's poly fleece version. When both are opened all the way, they can be zipped together to form a double-sized sleep sack. However, for Camino use, I prefer them one inside the other.
See here:
Oversized sleeping bag liner
<p>The Fleece Cover is a rectangle fleece liner that can be used year-round - as an accessory or as a standalone bag. It is a great "accessory," even if you already have several bags. It can help add extra warmth on those extra cold nights. As a sta
The fleece bag can also be used in conjunction with the microfiber liner - one inside the other - to create a layered sleep system. The problem is that this combination is not as compact or as light as a sleeping bag, per se. The advantage is that it is entirely machine-washable. It is warm even when damp.
My solution has been to bring the microfiber liner in all cases, on all Caminos. It compresses small and rides at the very bottom of my rucksack in a one-gallon / three-liter ziplock bag. If I need it it is there, with my emergency foil bivvy bag.
If I can get a blanket in an albergue or hostal, that is usually adequate, when used with the microfiber liner.
Depending on the conditions, I will wear more clothing layers, and sleep in my clothes. My wool socks, knit watch cap, microfiber gloves and fleece jacket usually do the trick in most cold weather conditions.
I started out, 11 years ago, using the SnugPak Traveller/Jungle Sleeping bag. An excellent choice. But, problems with the very fine fabric and zippers continually snagging caused me to seek other solutions.
Hope this helps.
Tom