If you want a simple 'one stop shop', the likes of Contracting Plus wouldn't be a bad start, or at least a benchmark to measure other options against. They'll charge a fixed rate, and look after everything; invoicing, payroll, vat returns, etc.
If it's something you think will last longer term, and want flexibility over timing of drawing money out of company, etc., then set up your own limited company. There's nothing to prevent you starting with the first option and setting up a company yourself later once you fund your feet.