Perhaps a 3rd solution.
A carefully placed large wormhole positioned in the orbital path of an inhabitable planet from a neighboring star would allow us to effectively steal a planet into our solar system.
It also allows us an escape route if something goes wrong with our Sun by operating that in reverse.
I like the gravity adjusting idea because it allows you to make fine tuned adjustments. But perhaps you could do the same with fine tuned planet sized wormholes.