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With the 240-watt power supply in mind, I'm going to give you some options.
Since you got the SFF model, you'll need a so-called 'low-profile' (LP) graphics card. All the LP GPU options I'll provide, come with the low-profile PCI bracket, which you'll have to use:
Here we go, from least expensive to more expensive:
There are obviously many other options, but this should give you an idea.
Kind Regards,
NonSequitur777