I've been thinking about this but am unsure if it's a good idea.
He could move in with you as a paying lodger - perfectly reasonable for a 19 year old lad. The Rent-A-Room scheme means you wouldn't be paying tax on the rental income if it is less than £625 a month. If he is entitled to UC then he will get help with the rent, considerably more than child benefit.
Claiming UC as a lodger is straightforward, but it can affect other benefits he may be entitled to. As usual, it is complex and this guide needs digesting
https://www.gov.uk/housing-and-universal-credit/renting-from-private-landlord
The amount of rent payable depends on where you live. In my area, for example, the maximum amount of rent payable is £91.82 for a single lodger. Use this calculator, choose 'shared accommodation' and put 1 person as the number in the household.