I have serious doubts about the bellis and polyanthus growing near Houston. Otherwise, you got some good ideas there. Other suggestions would be to sow a packet of larkspur (consolida) or Shirley poppies. You should be able to find a plentiful supply of snapdragons and pansies at your garden center too. Pansies and Snaps, plus dianthus, seem to be staples all across the southeast, and for good reason. If you plant your pansies in November (wait until your daytime highs are below 80 degrees), you should be able to enjoy them until April, depending on when your hot weather moves in. That's six months. Not a bad return on your investment. If you go with pansies, plant them six inches apart and for the most amazing look, put two plants in each hole (still six inches apart). Planted this way, they will completely cover the ground and mound up. Truly spectacular. Also, when you are buying your plants, buy the smallest most compact looking ones available in the six packs. Don't worry if they are blooming or not. The small ones will take off and give you the best, longest lived color all winter long. So, you could plant a circle of snapdragons around your shrub (even a double circle if the shrub is small this year), and then plant an edge of two to four rows deep of pansies around the outer part of the bed. The bulbs will come right up through the annuals. I would recommend that you consider a small EVERGREEN shrub for the center of your bed. That will become "bones" for the bed and will make a nice backdrop for whatever bedding and bulbs you want to do the rest of the year, even in the winter. A good one would be Indian Hawthorne, "Snow". It gets about four feet wide, but only about two feet high. It's neat, easy to grow, and is very nice when it blooms in the spring too.

I have broccoli growing here in central AR all winter long. I bought the plants and put them in the ground, probably before Christmas, maybe before Thanksgiving. Cold has not hurt broccoli or brussels sprouts and we've gotten to 17 F, maybe. They're growing slow, but the broccoli has the flower heads growing on it now, just not big enough to harvest. They are protected by milk jugs, cans or tomato cages with bird block not for the cold, but against the critters.

I don't see your two issues as a reason for replacing roses. Most of the roses people want have thorns. Mildew isn't a big problem compared to others. People replace roses because they are bored with them, they aren't performing well or are diseased. If you like what you have why go to all the work of replacing them. Are you looking for roses that don't require any spraying? Some people use cloud cover to fight mildew. I'm sure other posters will be abe to provide recommendations for thornless or mildew resistant roses.

Might be a caerulea hybrid--the coronal filaments on caerulea are generally straight. Incarnata and Incense have wavy filaments. Any of those species will regrow from the roots in the spring, but caerulea can stand up to more freezing temps before dying back than the other two. If you could post a pic, or describe the leaves, that'd help. In any event, you probably don't have anything to worry about.