I know it's not what you or I for that matter would want to hear if that is what I had to work with the SFF but the OEM's Dell / HP / Lenovo have made the SFF a pain to make into anything more than what they had intended it for it's projected market.
With out sending you down the rabbit hole trying to adapt the SFF you could for $100. off ebay get something more user friendly to make upgrades more normal.
But also a word of caution that also comes down to research on if a particular model Desktop Dell or other OEM's have road blocks on you may choose to buy.
Don't get me wrong SFF computer are great but as far as upgrades it's more or less a locked to design PC.
If anything the GT 1030 that
beyondlogic suggested and call it.