Write my company a legally binding investment contract

I am looking to have a one year legally binding contract written up between my Investment company and a potential client. Our investment company will be investing the clients money in to Crypto Currency with a guaranteed monthly return paid out to the client. every three months the percentage increases and At the end of the contract the client will receive their initial investment back. A break clause will be put in place that can be activated by either party after 6 months, if this clause is activated. The contract will be terminated and the initial investment will be returned to the client in full.