I used something called the Prenatal Cradle when I was pregnant with my
twins. It has straps that go up over your shoulders to help support the
belt, taking more pressure off the lower back.

similar to that is the belly bra, which I expect offers less support, but I
found it made a significant difference, it depends what type of support you
are looking for really, I could never tolerate any of the ones that went
just below the bump, despite trying several, whereas the bellybra seemed to
just mould to my body and help spread the weight of the bump and to then
take the pressure of the pelvis rather than the below bump style of just
tightening everything up.

Anne