plenum vs DSB ;)

What will be better for me:

a)plenum in sump from coraline gravel, it can be quite thick (15cm or even
more), main tank - bare bottom
b)DSB in sump (no possibility to buy live sand at all, so only dead
sand+worms from live rock)
c)plenum in sump, and sand in main tank (tank is only 35cm height, so no
real DSB, maybe 3-4cm of sand max.)

a - the cheapiest method (sand is quite expensive here), high flow in main
tank without problems
b - worms must migrate from live rock only, i will not be able to add new
worms, expensive sand, but recently very popular method
c - cheap plenum, thin layer of sand can hold some worms (probably better
then plenum), but high flow can move sand all over the tank