The lack of curved tail feathers on a sebright rooster is due to hen-feathering. So it’s probably not possible to get what you want, unless you bred in hen-feathering (from sebrights, campines, or henny gamefowl) and were fine with all your roosters having the same coloring as the hens. The tail...
I agree that you should cross your existing hen to another rooster rather than trying to recreate her altogether. Crossing her to any rooster with penciling/partridge will most likely produce mostly penciled chicks, either silver or gold depending on the father. If you cross her to an isabel...
Your plan to breed both roosters is a good idea, since they could carry partridge, but you won’t tell until you’ve bred them. Ideally, you would use a pure partridge rooster, but those other two should work as well (it will just take longer to set the color).