My Dd is only 8mo and has just had a cold preceded by a gastro type bug. The gastro didn't seem to bother her at night, but the cold did. We had a few nights of being up and down a lot with her, mainly because she couldn't breathe, but she has gone right back to her routine now. I think once the routine is established, then unless it is seriously disrupted, they have already learnt all the right building blocks so to speak.
Even though DD was awake quite a bit in the night when she was ill, I still kept the lights low, quiet talking/hushing etc. and rocking (which we don't normally do), and then morning was morning and lights on etc. Once her nose was clear again, she went right back to self-settling and sleeping through.
TBH, I don't sleep that well when I've got a cold, it's horrid. It's easier for him to sleep on you because it's comfy and reassuring, like we all need a hug when we're poorly.
D
PS, try propping one end of the cot up so he's not lying completely flat (like I need more pillows when I have a cold), and also calpol and olbas oil are your friend. Olbas oil is actually great for clearing the nose without actually 'medicating' so to speak.