Do you want a booster to extend the wifi range or get a device to replace the old router and work with the ATT network?
For the former one, there are some network expansions: https://www.tp-link.com/en/products/list-10.html https://www.tp-link.com/en/products/list-18.html https://www.tp-link.com/en/products/list-12.html
For the latter one, what kind of device do you need? like the DSL modem router or the wireless router? More details will help a lot.