The only way you can get more comfortable / softer suspension is by fitting original Opel/Vauxhall shock absorbers.
B4s (which I have on my car) feel great, and I'm surprised you have had problems with them. They are a
little harder than standard, but not so much that the ride becomes uncomfortable. They do harder/sportier versions, B6 and even B8s. If you find the B4 hard, then just imagine what the B8s are like!
To be honest if you find your suspension 'bad' with B4s, there's nothing (apart from original dealer shocks) which will be more comfortable. You could consider fitting Elite (called the MV6 in Europe) self levelling rear suspension, which is a little softer, but you will need springs, dampers, the pump and sensors too.

You are asking about springs and dampers, but are your wishbones, droplinks and bushes in good condition? These also affect the ride.
