kudos to you - I confess that these are one of my (many) plant fails....even the common (and supposedly easy) white zantedeschia link off to plant heaven after one measly season....ho, and those expensive rehmannii and elliottiias are goners within weeks of my tender care. And you had a dozen to cut off! Lucky if I managed 1 ot 2 so yours must be thriving.For those who can grow them, they do seem to be tough and forgiving - I see clumps of them in the neighbourhood, doing well with no visible signs of care and attention (to my extreme annoyance).
Tricky to arrange a support system - they are not really amenable to paeony hoops...but I expect someone who actually CAN grow these will come along with some useful advice.

I bought a few on clearance about a month ago. They looked great. About a week after I planted them their leaves turned yellow and died. Some are regrowing leaves.

These are a "do nothing" plant for me (sorry campanula!) I've never needed to stake them, but mine have never gotten crazy tall like some I have seen in my neighborhood. I would think two stakes and some twine would do it, just something for the top of the plant to lean on. I'd suggest tomatoes cages but your sound too big for them.

I'm wondering if a large peony hoop would work. Maybe it's too late this year?
I still haven't cut off the bent stems. I thought I'd see if they stay green.
The plant WAS 2 to 3 feet tall!

When I lived on the coast, they grew and flowered with no help at all,many very old, most predating my purchase of the property. Here in the very dry, very warm, Napa valley, they will only survive if you are lucky enough to find just the right spot in your garden. I have some in two gardens that survive and bloom but with very little enthuseism, both patches about 10 years old. Al