It seems that men tend to sleep hot and women tend to sleep cold. I ordered the warmest Sea to Summit sleeping bag liner, took one look and sent it back. I knew it wouldn't suffice for me. I sleep with a light duvet in summer in the UK.
I think it was you,
@trecile, who posted a photo of your sleeping setup and that's what works for me, with the addition of the ever-wonderful sarong, which functions as a privacy screen at nights (I always have a bottom bunk, I even prefer that to a single bed in a dorm just for the privacy).
Here's my sleeping bag:
https://www.amazon.co.uk/gp/product/B01CEVT922/?tag=casaivar-21
Here's the sleep sack I've converted to a mattress + pillow cover:
https://www.amazon.co.uk/gp/product/B071W5VHQJ/?tag=casaivar-21
All my 'sleep system' gets stuffed into a 5-10L drybag (everything treated with Permethrin, of course), the last thing to go into the rucksack in the AM.
I will admit that when you're jammed into one large room with twenty other pilgrims and no open window it can get hot and stuffy, so I will just stick my feet in the bottom of my sleeping bag and not cover entirely. I don't walk June - mid-September, More than just the dorm rooms would be too hot for me.