I’ll try another Riley...
My prefix is a unit
My infix relates units
My suffix is found on shore
My whole always makes more
Bonus: My uffix is my whole
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My prefix is a unit
My infix relates units
My suffix is found on shore
My whole always makes more
Bonus: My uffix is my whole
I think the answer is
Ampersand
My prefix is a unit
Amp, short for ampere, unit of electric current
My infix relates units
Per, e.g, kilometres per hour
My suffix is found on shore
Sand
My whole always makes more
The use of "&" implies there's more to come.
My uffix is my whole
And is equivalent to &,
as @Fifth_H0r5eman points out "uffix" is the end of suffix so this works.
also, as @Rubio points out, "uffix" is suffix without the 's', the same as sand/and.