Not a lot of really small 50's in that mount, but there is a CZJ Tessar F2.8 that is very compact, it was made for the Praktica cameras. If you want to keep it Pentax (and why wouldn't you) you could find a Super Takumar 55mm 1.8 that is a great lens and should be very cheap. The 50mm 1.4 is also a great lens and really no bigger than the 1.8 but some SV models wont accept this lens due to the mirror fouling the rear element. If my memory serves me correctly, the later SV's would take the 1.4, but I could be wrong here.
The SV, although having a somewhat dimmer viewfinder than later cameras is still a sweet classic and you will enjoy using it.