I just had a look at this guy's website....
Apparently contact with parents is a 'reward' and should be withheld overnight to ensure sensible sleeping patterns.
ok.
Oh boy...

Well as for him being as 'expert' ... you're the mummy so I figure YOU are the expert on what your little guy needs and what works for you both.

It's normal for babies sleep patterns to change, they might go from sleeping well, to not-so-well, back to well again & then change again.
Or they could do what all my kids did... start out so-so & get worse

Truly, I have had 4 'bad' sleepers. They do all sleep through eventually. 18 - 22 months seems to be the magic mark for us. It might not be what you want to hear right now (although your little boy might be complettely different, too) but really it's like the end stages of pregnancy - hard & seems endless at the time, but gone before you know it.
Trust your instincts hun