Being a very busy sole trader is a different world to running a business. I think your office assistant is a great step forward but she may end up making you even busier. It costs money to grow a business and staff too. To grow you need to have the staff before you win the work and as everyone says its better getting two part timers for flexibility, but I do not agree with part time office/cleaner as she will only end up like you......being so busy doing the cleaning work she can't focus on growing the business from the office.
Marketing the business, caring for the clients, attending network meetings,organising staff rotas, staff payroll, staff cover and then the most important part getting the invoices out accurately and on time to insure the cash flow is strong enough to support the new business she has brought in leaves little time to clean.
Increasing your prices might be enough to cover the additional office/admin costs needed to grow a business but you will be as busy with less actual cash for yourself, it takes a while before either your work load eases or your income increases.
But it is worth every bit of hard work.....I'm lying here typing this in the bath and by the time I finish it I (the business) will have delivered a £72 net profit.
Best of luck
Gordon