Student or Learner
As a general rule, we use -er for one syllable adjectives and more for more than one syllable adjectives.
And we use less for more than one syllable adjectives, e.g. less beautiful.
But how about one syllable adjectives? I mean can we use less with one syllable adjectives? Can we say "less busy" or "less nice"? If no, what can we use for one syllable adjectives?
There is no helpful suffix which indicates "less". As you said, we simply put "less" before the adjective, regardless of the number of syllables in the adjective.
This apple is less green than the others.
My jumper is less stripy than yours.
Her essay was less complicated than she expected.
However, I should point out that, in many cases, instead of using less + adj + than, we often use not as + adj + as.
This apple is not as green as the others.
My jumper is not as stripy as yours.
Her essay was not as complicated as she expected.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.