The tube anemone is aggressive and grows large. Probably the width of the tank.
If you want something colorful and flowy and like a mini anemone but safe, consider a fathead dendro. Super easy to care for, neon orange, yellows, and red, doesn’t care what light you use, eats flake food and frozen mysis. A little colony of this would be sweet. The fat head dendro is 1-2” per head and you start with one and they will multiply slowly
Size reference to zoa polyp
Leave some open sandbed space and a donut style coral like Cynarina, scolymia, or moseleya could be a killer centerpiece that’s easy to care for
And at night they do this