I am thinking of making an area of raised beds on my allotment to grow salad items and herbs etc and was considering using old scaffold boards or wood to make the frame and sides, is this a good idea?

Should I treat the inside of the wood with something to stop it rotting, or should I just leave them and fill with earth?

Also on a side note, if I may also ask? What is the best type of soil to fill the raised beds with if I intend to grow things like rocket, spinach, thyme, tomatoes, spring onion (scallion), callaloo etc?

Any advice would be greatly appreciated. Many thanks.