Carrier-side forwarding is the traditional route: you activate it in your home carrier's app or with a dial code before or after leaving, pointing calls at your full international local number. It's simple and works on any phone, but understand the billing: you typically pay your home carrier's international rate for every forwarded minute, so it suits people who receive occasional important calls, not chatterboxes. Conditional forwarding, only when unanswered or unreachable, is a nice middle ground that catches calls when your home SIM is offline.
App-based dual numbers are the cheaper modern path. Services like Google Voice, where available to you, give you a number that rings over data on any connection worldwide, free or nearly so. The limitation is eligibility; many require signup from a supported country, so set it up before you move.
Whatever you choose, test the full loop, including SMS delivery, before you rely on it for anything important.