There is no actual "template" for a Separation Agreement, and personally, I would avoid those sites that offer you such a template.
The division of assets/liabilities is a serious business, and you should consult a Family Law sols. Once a SA is registered, it becomes a legally binding document, and there is very limited scope for altering/changing/removing any of the clauses contained within (except for those relating to the children).
I take it you are concerned about costs?
To keep legal costs down, the more you and your wife can agree on between you, the less the sols will be involved in the to-ing and fro-ing that occurs during negations.
Bottom line is - always get your draft SA checked over by a Family Law professional.