Small hotel (around 20 rooms) seeks hotel software

We are a hotel in southern Germany with around 20 rooms, including single, double, triple, and quadruple rooms. We mainly cater to business travelers. We are looking for hotel software to support our daily workflow with the following requirements:

• A reservation system that is linked to various emails (offers, confirmations, arrival information on specific days)
• Invoicing
• The individual forms should be customizable
• It would be useful to be able to manage the hotel rooms available online, although our main goal is direct sales (we only have around 20% listed on HRS, and more in quiet weeks)
• We do not want guests to be able to book directly for the time being - our ideal guest books directly and stays for more than one night
• It should be possible to assign guests to a company and also to different company rates
• Windows-compatible

This is a software workstation.