Ok so I have heard it pronounced a million different ways- no one seems to know for sure how to say it! So what is the deal with the name [name]Callum[/name]?!
Also what do you think of these names-
[name]Noah[/name]
[name]Isaac[/name]
[name]Levi[/name]
[name]Lukas[/name]
[name]Camden[/name]
[name]Ryan[/name]
Those are my favs right now- I am also game for some suggestions!
Everyone I know just pronounces it Cah-lum.
I like [name]Levi[/name] on your list. [name]Ryan[/name] is good too but maybe a bit popular. [name]Camden[/name] ([name]Cam[/name]) is quite nice and [name]Lucas[/name] ([name]Luca[/name]) too
I’ve only ever heard CAHL-um or CAHL-lum.
[name]How[/name] else have you heard it said?
It’s my brother’s name, well, [name]Calum[/name] is. It’s pronounced Cah-lum, like the PPs said.
I knew a family who had named their son [name]Callum[/name] but pronounced it Col-um (rhymes with Gollum). [name]Imagine[/name] naming your child and mispronouncing it for the kid’s whole life, so embarrassing! Also, the family claimed to be Scottish, so you’d think they’d know how to pronounce a Scottish name, but apparently not…
I have heard it ‘Cahl-um’ as in [name]Calvin[/name]. ‘[name]Cay[/name]-lum’ as in [name]Caitlyn[/name]. ‘Cawl-um’ as in column. And everyone seems to have a different opinion on how it is pronounced!
It’s definitely just Cah-lum.
[name]Cal[/name]-um, [name]Cal[/name] as in [name]Calvin[/name]. I love it. 
I have only heard it pronounced Cah-lum, a lot like [name]Calvin[/name] if that helps? I also like the spelling [name]Calum[/name]. 
From your list I like [name]Isaac[/name], [name]Levi[/name], and [name]Lucas[/name] (spelled this way, and you might also like [name]Luca[/name] or [name]Lucian[/name]). The others are ok but just too trendy.
Good luck!