There are two main ways to approach this:
1. The company can sell the business, which in this case consists of the goodwill and the rights and obligations under the contracts BUT they will have to be assignable, which may depend on the terms of the contracts
2. You can sell the company. Simpler from your perspective, more complex from a buyer's perspective.
Unless you are talking very small money (less than €15k) you really cannot manage without professional advice. I have seen some very small transactions where the parties just handed over share transfer forms and the buyer took over the company with minimal paperwork, but it is not something I would recomment.
I doubt if any competent solicitor would deal with a share purchase agreement for less than circa 2.5k plus VAT and it could very easily run to 10k plus VAT.