Most people will want to do something useful to supplement their basic income because it will only be enough to pay for the basic necessities. Would you want to live like a poor student for the rest of your life, renting a bedroom and being only able to afford thrift shop clothes and ramen noodles? Most people aspire to have their own place, date other people, have friends, etc. Most people have some minimum amount of drive for status. That will ensure that they make some effort to rise above the bare minimum.

As for how to pay for this, consider that central banks have printed trillions of dollars and basically handed that money to corporations, bailing them out of their debt. We live in the world of corporate welfare. We could expand the money supply and give that money to the people instead. In some ways, this is more capitalist than the alternative. Why? Because corporations who get too far into debt should die. If you give money to the people, you at least ensure that corporations will have to sell people something that they actually need/want, instead of being able to count on a corporate bailout.