I think it's the side shoots that are curly, not the top of the plant, or not until it's gotten bigger anyway, if I understand your question right. I picture you growing the plants just a few inches tall then wanting to harvest them, is that right? The shoots you're picturing come from older/bigger plants and if you pinch them back they
should get bushy and grow more side shoots, like basil does. I would stick with the sweeter peas, but I've never tried field pea shoots.