Need software or Spreadsheet

Hi I am new to the site and very glad to have found it!

I have started managing a small hotel in Phuket, Thailand.
The frontdesk/ reservation system that is in place now is to say the least a mess!

What I am looking for is either free software (the owner is super cheap) or an excel spreadsheet to manage reservations, occupancy and payment.

It also has to be super easy/ dummy proof. I love my Thai staff but the education level is not the best.

Any help would be very much appreciated!

Thank you in advance.