Here's a quick way to draw consistent wavy lines. The same technique can be applied for springs.
This isn't intended to devalue your request for a precise geometric tool for this kind of needs, which i agree it's quite useful.
It's just a way to help you solve the problem with the available tools/resources we have at the moment.
because you need a transparent image at the end, I think you have to cut out the spaces. I don't know if it is the right way but you can achieve it like this...
(since we still don't have an offset tool, we have to use expand stroke)
1. write your text, set stroke width and align stroke to outside (stroke width will determine the space between your text and your lines later)
2. convert your text to path and go to Layer -> Expand Stroke (I've switched off visibility of the black text in the screenshot)
3. draw your lines with your appropriate stroke width; highlight your lines, go to Layer -> Expand Stroke and set Geometry -> add, now you have one "line-shape",
make sure your line-shape is underneath your text
4. highlight the line-shape and all the expanded strokes -> Geometry -> Subtract
5. now you have a cutted line-shape
6. Geometry -> divide and delete the small pieces
7. you're done ;-)
Welcome to Affinity Forums :)
To display multiple documents at the same time you have to change to Separated Mode (menu Window ▸ Separated Mode).
To switch between document tabs press ⌘ (cmd) + `