Dell Inspiron 7520 HDD+SDD - whether downgrade from Windows 10 to Windows 7 will be possible?

Hello,

I have quite old version of Inspiron 7520 that was shipped with OEM Windows 7 and one HDD only. Now I bought a SSD and found that I can't just reinstall my OS to the new SSD:

• I have no DVD with Windows 7 (it's OEM version)
• Dell backup and recovery tool say that backup can be created on external HDD only (I have no external HDD), so I can't boot from an USB device
• Microsoft site doesn't allow to download Windows 7 (.iso) because my product's key belongs to OEM version

So - as far as I understand - I have two* possibilities:

1. Probably not the best
   1. Try to find an Windows disk image
   2. Install it on my SSD
   3. Activate it by my current key
2. Probably not the best too
   1. Download a Windows 10 bootable image
   2. Install it on my SSD
   3. Activate it  by my current Windows 7 key (because upgrade from 7 to 10 is still possible)

The second case looks more legal :) but what if I'll find that Windows 10 is not usable for me?

So, here is the question: can I legally switch to my HDD drive with original Windows 7 (or restore it from the original backup partition) after upgrade to Windows 10**? I'm not sure about all these features with saving Windows' key in BIOS and so on :)

* Did I miss another way to move OEM Windows 7 to a new SSD?

**Sorry if such info was described already, it's not easy to find my case exactly...