Iris multiply, but it's pretty slow, and they won't really climb out of the bed. But if you're thinking tall bearded iris, hopefully the bed is against a wall; the wind tends to knock them over unless they have some sort of support or shelter. If it's not against a wall, get a smaller type of iris. Another possibility is day lilies, they start blooming around the same time as iris (both are just starting now, mid-may, in zone 6).

Hmm, its not against a wall. Don't know if I have the space for daylilies

What about some ornamental alliums such as 'Purple Sensation'(blooming now) or 'Globemaster' (larger and later-blooming)? They don't take up much room and will give you the height you want. Another bulb that is blooming now for me in part shade is camassia.

I have loads of TB iris and none of them have ever fallen over and they most definitely are not against a wall or even near the house. i do believe that they are your best bet but they are not a plant that you can forget. they have to be manitained to keep putting on a good show. the dwarf varieties tend to bloom a bit earlier than the TB's but there's a wide range of colours. however if you're lookinf for something about a foot-and-a-half, eiter stay with standard dwarf bearded (SDB) of border bearded (BB).

also, peonies might be a viable option but hey can get taller as they age and can be up to 3ft across, but this would take a number of years and they require far less maintenance than irises, as they never really have to be divided to keep up flower power and have few pests (irises have borers and root rot)

Why don't you try some of the smaller daylilies such as Aztec Gold (16") or the reliable Stella D'Oro (12")?

What if I planted tulips with Papaver orientalis? The space is about 2 by 5 feet. I could trim down the papaver foliage after blooming correct? How big/wide do these get?