A picture of your garden would help with suggestions.

"Dwarf" lilacs are not the same species as old fashioned common or French lilacs. Not much color choice, much smaller flower clusters and while still fragrant, not the same overwhelming lilac scent.

btw, dwarf lilacs play well with most other plants. The iris and ditch lilies will not be an issue, although I would keep the clear of the area until your lilac shrub becomes established.

How damp is the planting site? Because full of ditch lilies and blue flags sounds like it is a moist area. Which a lilac won't like, unless the drainage happens to be good enough for it anyway.

Otherwise Syringa meyeri 'Palibin' is a good one which although eventually medium sized is recommended for small gardens because it is slow growing, has in fact been called dwarf Korean lilac in commerce. But as mentioned above lilacs having small tight growth habits in combination with the flower power of common lilac (S. vulgaris) are not something that is usually seen.