Anna,
You could advertise and interview then when you get really busy give them a call.
When you do need to get someone, give them a trial period, as from experience, a person at an interview is not the same person you employ.
You can join the Federation Of Small Business, they have a free helpline for all the issues you encounter when starting up, employment, health & safety, tax, etc.
They have a wesite just type in FSB.
Keeping good staff, is difficult, look after them and they will look after you.
Catman