The answer words to this flat differ only by a single letter, as indicated by the cue words.

The town hosts a mixer each Saturday night,
For those with no husband and those with no wife.
Those who are WEIGHT are encouraged to HEIGHT,
And perhaps find the one - the love of their life.

Answer:

Those who are SINGLE are encouraged to MINGLE.

Credit:
The Enigma 
NPL Magazine
October, 2019 
A. CHEMEM