Populate select input via static values on plugin settings page
If your first attempt – using a variable method – failed, it was probably because you had the "path" to that variable method wrong. If your variable method is called getOptions() and resides in a variable class called MyPluginVariable, the path should be

craft.myPlugin.getOptions


not

craft.myPlugin.settings.getOptions


Anyway, your current solution is fine. The ideal, "Craft-y" way to do stuff like this would probably be to keep the input options in a plugin config file and use a service + variable method to expose the data to the template – but for such a simple case there's really no need to over-engineer things. If you have more fields/options later, or need the data to be dynamic or stored in a database, deal with it then. Don't optimize too early.

Personally, I'd consider just hard coding the options in the template:

forms.selectField({
    'label': "myLabel",
    'instructions': "My Instructions"|t,
    'required': true,
    'id': 'myInput',
    'name': 'myInput',
    'options': {
        '' : 'Select',
        1 : '1',
        2 : '2',
        ...
    }
})