Hi fortune
I would use a reputable care agency agency.
I would want to meet the carer beforehand to make sure they were a good fit for your Mum and introduce them in the lead up to the stay.
I would ask lots of questions based particularly on the needs of your Mum:
What provision is in place for covering sickness (of the carer).
How would emergencies be handled.
What their approach would be in certain situations, eg calming someone down, agression, etc
It's more difficult without knowing the situation with your Mum, for example if she is used to having carers. We tried a live in option with my folks for a week, which ended in an altercation. With hindsight the carer (who was independent and came through a recommendation) was out of her depth. I don't mention this to put you off, as live in is a good solution and important for you to be able to go away, just for you to be thorough in your search.
I hope you are able to find the right care. All the best. Georgina