Absoloutely anything. I use Hazel sticks, bamboo canes an old fence post, trellis.
You can use anything so they can scramble up them.
Tie them in to begin with until they climb away. Once they are flowering, take off the old flowers so the energy goes into producing more flowers rather than seed.

I have bought some pea netting, only cost me a £1, so am hoping they will like it :O)

Should work Blooming

I tie a wigwam of bean sticks together and they love this, anything like that will do and pick them frequently and enjoy the scent indoors. :o)

You can be as fancy or basic as you like - I've seen gardens where folk have spent a lot of money to support their sweet peas others where they use twiggy branches and other 'free' supports - it just depends what you want your garden to look like. Our peas tend to be grown through twiggy branches... cost nothing :-)