Mike's simple, opensource licence while I search for a suitable standard one...

Copyright (c) 2021 Mike Foster

Permission is hereby granted, free of charge, to any person obtaining a copy
of this Software to deal in the Software without restriction and to permit persons
to whom the Software is furnished to do so, subject to the following conditions:

1. You do not provide others with an ability to avoid or circumvent the terms of this licence.
2. You do not claim the obtained Software as your own work.
3. You attribute the author and link to the Home Repository of the Software.
4. You obtain written permission before selling the Software or a derivative work.
5. You obtain written permission before refering to the author or Software in any marketing or advertising.
6. You don't blame the author if anything goes wrong.

To avoid doubt: the Software consists of everything checked in to the Home Repository
And yes - hosting the Software as a Service would be an example of a derivative work ;)