They sell a cylinder shaped cage made out of fencing material and depending on the size of your plants you may want to add a stake to keep the main stalk centered in the cage. Westlake sells both items.
There is no way to keep it tomato plant straight. Unless you take all of the extra limbs off of them. But they are what sets on tomatoes. To keep them up straight you're going to have to tie them up to a fence if you have a lot or a tomato plant cage. You can stake them but mostly the stakes fall over when they get heavy with tomatoes.
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