Hi - I hope its ok to post this here...
This sounds really interesting, as I thought the storage couldn't be upgraded? (I'm extremely non-technical with this stuff and Google results are conflicting). I'm having similar problems to the OP where the storage runs low and I use my Macbook in a similar way. To be clear, the upgradable storage your talking about is the same storage you see when clicking "About this Mac - Storage"? If it is possible, how difficult is it to do? I've someone who knows their way around Windows computers and upgrading storage, but not Macs and I'm super nervous about handing it over to someone to do in case they damage it...
And if I would buy a new one, is it more important to have the i3 or i5 model, or does that not really matter? Currently I have:
1.6 GHz Intel Core i5
4 GB 1600 MHz DDR3
251GB Flash storage
And its been actually great up until the last 6 months or so with storage and super slowness/lagging. The wheel comes up and stays there for a very long time, and I get more and more toolbar messages that the site I'm on is causing the Mac to slow down (sites like Canva or Squarespace). Is this something that your option of upgrading can fix?
Thank you!