This, for £21.99, would do the job:
Amazon.co.uk User Recommendation
You'd also need a Scart lead, plus you'd need to know how to switch the TV's input so that it shows the output from the Freeview box. Once you've done that, you just leave your TV on that setting and switch channels using the remote control for the Freeview box.
[Note: You can often pick up Freeview set-top boxes, with Scart outputs and complete with their remote controls, very cheaply in charity shops].