Well it's like when you're in maternity, it's actually boiling! Must be exceeding 26 degrees at least i'm sure and they shove two blankets on your LO! Just before I left the midwife told me "Remember if it's below 18, two blankets, above 18, one blanket" Errr... really?! lol
I use the sheet/blanket guides on mothercare/mamas and papas guides, LO seems to be just right by these guidelines though it does prove to be a bit of a pain in the ass when i'll go to bed and our room's 21 degrees, wake up in the middle of the night with her having kicked off some of her covers (tried a sleeping bag but she's too small for it at the mo) then i'm having to add a blanket so generally just have a sheet & two blankets on from the offset and she doesn't seem too hot to me.
Just all depends on the individual child really, I hate it when they say "LO needs one more layer than what you do" but if this applied to DH and me we'd be forever dressing her up and down between us! lol! I feel the cold really bad (especially since not being pregnant, brrrr!) and DH works in the outdoors so feels hot regularly (though with my coldness I am starting to desensitising him slightly as I like the heating up!)
Just one more thing in the world of baby that there's no set of rules for!
xxx