Dear madam,
Any agreement is enforceable in a court of law. Other than writing, even if a claimant could prove in a court of that a verbal agreement was made, that is also enforceable .
Now the difference is,
Basic
if you choose to execute on a plain paper or on a letter-head by the concerned parties only, again with witnesses, again with non-partisan witnesses.
Further,
again the same choices as above on a stamp paper
still further,
the same choices as above on a stamp paper and registering the agreement with the registrar.
The enforceability becomes stronger. And your legal counsel could guide you further professionally, that with each stronger options, you may be able to charge more severe laws for a breach.
I guess this meets your query to some extent.
regards.