Online services to help people draw up such agreements are springing up. The enticement of these services is an agreement done on a DIY basis at low cost. But before launching into such a DIY agreement, beware. As with all things, you get what you pay for. Any kind of legal contract may have implications which the parties may not appreciate. Once agreed by the parties the terms of their agreement may be binding on them even after they separate; perhaps in ways they had not entirely intended or understood at the time they entered into it. Unlike married couples, there is no general law permitting a court to vary most of the terms of a contract or trust which unmarried parties have created between each other.
Tempting although a cheap online agreement may be, do not underestimate how complex the issues may be. Investing in a family lawyer to provide some advice based on long experience and wisdom and to draft the agreement may seem comparatively expensive compared to the DIY option. However, experience shows that those costs pale into insignificance when compared with the consequences of trying to unravel a poorly thought out and or ill-drafted agreement years later.