Soft boxes seem a little over the top for your needs. Where soft boxes are concerned, the bigger the better.
The better ones have a diffuser in the middle as well as the one at the front. They also eat a lot of light, so
fairly powerful flash heads are needed. You will also need a fair amount of room to use them.
They genraly fold up for storage though. Another alternative you may wish to look at are beauty dishes.
Ive not used them myself, but Ive seen the pics and Ive heard they are very good.
Just google beauty dish, Im sure you will find them easy enough.
They could be just what you need !