Yes - two syllable adjectives are nearly always "flexible", in that they can form the comparative/superlative with either
-er/-est or
more/most. That goes too, incidentally, for adjectives ending in "y", which textbooks will tell you "always" become
-ier/-iest. Not true. Here are some examples found on the
Collins concordancer :
... it doesn't make you any
more happy,
Conservatives on the opposite wing are no
more happy.
`I'm feeling healthier,
more happy with myself and just in general," she said. `
...he found women hard to fathom and was
more happy in the company of men.
But there's other things that I'm
more happy about--
In Ulster I met the
most friendly, hospitable people in the world, but I also
... impressive and important. We parted in
most friendly courteous fashion.
... for this must be one of the
most friendly places on earth -