You can use a large pot. Mirabilis is perennial, so the pot may need to be changed over time, to a bigger one.
Yes, the beautiful white-lined sphinx, Hyles lineata, is this plant's symbiotic [mutualistic] partner. If stems grow too tall, simply set in some stakes for it, to keep the weight centered.

I grew them in five-gallon buckets last year and was pleased with the results. They got about 3 feet tall and I did need to stake them. They bloom on the growing tips so it's better to pinch them early in their development than to prune later on. You don't want to cut off all the flower buds just when they're about to put on a show.

Edie

Thank you for the encouragement and growing explanations. I will give them a try in a big deck pot, remembering to pinch back when small. Maybe by doing this, I can keep their size more manageable.

~Mary

I'm giving it a try. They are brave plants. Some people have even turned old plants into specimen "bonsai".