I have a form created with the breezingForms extension for Joomla. I'd like to store the currently logged in user's name with the form. I don't need to continue to use the same extension. However, what we like about that extension is that it has a form builder that doesn't require code.
If you don't need to use the username for something else (which might require coding that you're trying to avoid), I know that RSForms has global placeholders for data it automatically saves for the form. That includes username if the user was logged in.
RSForms Pro also has a set of global placeholders (see https://www.rsjoomla.com/support/documentation/rsform-pro/getting-started/component-emails.html) should you need to display the information later (eg thank you page, admin email, user email).
The Crosstec post by @FFrewin gives a perfectly adequate solution that would be common to calling the user information from the Joomla API into any content.
However, a little bit of code would not be something I'd be shying away from as that's where the power of the Joomla API often lies.
Out of curiosity, what's the reason you're not wanting to get out of Easymode? That may expand how to create a workaround using extensions like a combination of Regular Labs Snippets, ReReplacer and Sourcer to create your own mini plugin calls.