do you want to use the thinkpad for just live use or everyday use with lots of other programs and files ?
You can go for 256GB(+) mSATA SSD if the firmware will take it.
The tiny thinkpad is the computer I use everyday everywhere.
I have a (poor) DAW note at home. i5, 8 Gb, 1Tb HD....
So, maybe, upgrading the thinkpad is not the idea; a bit expensive upgrade for the little notebook and its use.
I was thinking to have the BIAB available into a very fast external HD, so I thought it would be a good idea to use the usb3 SSD.