Revolut have partnered with Bitstamp to provide purchasing of bitcoin (and some other crypto). They also have a cashback feature where one can opt to receive crypto. The percentages are not huge, but every little bit helps. Then they have feature whereby upon making a purchase, the amount spent is rounded up (a multiplier can also be applied here) and the amount converted to crypto and stored.

The only negative currently is the limitation on not being able to withdraw the coins to a personal wallet - this is a fully custodial service. Only conversion to fiat or spending from the funds is permitted currently. Spending the funds involves a crypto->fiat conversion being performed without user input.