Having CBs in the forecast just means be careful - you can still fly safely. The CB tops don't have to reach the stratosphere. They tops can can be from 10000 to 35000 (usually they are just above my svc ceiling!)
If they are not embedded then just keep your eyes open and fly around them giving them a wide berth.
If the CBs are embedded with tops below your svc ceiling then go over the top of them.
If they are isolated and the general cloud tops are below your svc ceiling then fly over the CuSc and avoid the CBs (you will see them sticking up - usually right along your route of flight and nowhere else!)
If they are widespread and embedded in a front or trough and represent a solid line that is not practical to route around then I would either plan a later departure or get as close as possible, land and let the weather pass over the top.
If they are very isolated and you have a stormscope / weather radar or preferably both then you can pick your way through but it can be rough and very icy in there.
I would recommend Richard L Collins book "Thunderstorms and Airplanes" - it dispels some of the myths about CBs.
SB