So sad when hedgehogs die. Our solitary garden hedgie died at the vets (old age and disease) and we haven't seen any now for over ten years. Their numbers are declining. Slugs can be defeated with bottle cloches, bell cloches, and rings of copper around sensitive plants, as they don't like crossing copper.
Collecting them manually and putting in a bucket with strong salt brine solution will kill them instantly. A not-so-squeamish gardener kills them with scissors - halves them with one deft snip. During the day they shelter from the heat under a piece of wood and can be collected up.
If plants are planted out when they are a little bigger, they often survive a bad slug attack. They get half eaten rather than killed. Red lettuce is less attractive to slugs than green lettuce.
There are organic slug pellets. Wilko has some that are quite affordable, if all else fails.