C. retro easily gets to 2'+ and is rather invasive. I started with one and now it's all over my tank. A beautiful plant nevertheless.
C. wendtii (green/red/bronze) regularly gets to 14"-16+" tall and is another slim-leaved, prolific plant.
If your Rotala Rotundifolia is doing well, I would try Limnophila aromatica/aquatica/sessiliflora, Green Cabomba, Didiplis diandra, regular Baby Tears, even your common Egeria densa - but they are all fine-leaved plants. Bacopa caroliniana or australis would be other candidates.
Another idea is Vesuvius (Echinodorus Angustifolia): leaves are more towards what you looking for, gets ~14" for me and grows just fine in very low light.
Hygrophila corymbosa Angustifolia - can get really bushy but is easy to trim.
Sagitaria subulata or Echinodorus might be a tad too large for your tank.
Neddle Leaf Java Fern (some sp. get to 16"+)
Just my brain dump