As suggested by the previous poster, you can use an external USB3 SSD. Other options include:
- Using an external Thunderbolt SSD - presuming you have a free Thunderbolt/DisplayPort port. These can be expensive but a "cheap" (relatively) option would be the LaCie Rugged Thunderbolt HDD (refurbished by LaCie/Seagate makes it even cheaper) and replace that with a SSD. I've done that although I don't use it as a boot disk. Look on YouTube on how to replace the disk - there's work involved but it's not difficult. The advantage of the Thunderbolt SSD is you get TRIM and SMART and you're not sharing the USB I/O with other devices. Whether these are worth it is a personal decision.
- Use a M.2 PCIe NVMe SSD. I started the following thread on going this route. This involves much less work. If you go this route, please post back - there's some tips on SSD choice on SSD's that have appeared since I started the thread. (This would involve buying a new SSD.)
https://forums.macrumors.com/thread...in-the-2014-mini.2118732/page-2#post-27166599
- Have an Apple-authorized service provider do the work. The cost would probably be at least $50.
I've done the SATA disk replacement on a 2012 and 2014 Mini. The second time was much easier than the first. People have botched the job so your concerns are not misplaced. But many have done it successfully.
If your HDD is original to your Mini, it's about time you had it replaced. The Apple OS's have become more and more geared towards SSD's. If you have the base 1.4Ghz model with 4GB RAM, then what could be slowing the computer down is the 4GB RAM, which may not be enough for what you want to do. In that case, you can't upgrade the RAM so could still have slow performance even after a SSD replacement. But if you have sufficient RAM, a SSD will very likely result in noticeable improvement in response time.