Hydrangeas (with very minor exceptions) are deciduous - they lose their leaves during the winter - so perhaps what you have is something else. What you are looking for are broadleaved evergreen shrubs - things like rhododendrons and azaleas, pieris, escallonia and many others. Most nurseries or garden centers are set up so that plants with similar characteristics, like being evergreen or preferring shade, are grouped together and this is a good place to go to get ideas of what you might like to include. Avoid places like Lowe's or Home Depot until you become more familiar with the plants and know what you want - typically, their selection is limited, their staff is not particularly knowledgeable about what they offer and how to tend it and they are not set up in a similar fashion with like plants together. In general, most evergreen shrubs have a pretty limited bloom season, so you may want to include a few deciduous ones as well that extend the period of interest with flowers at different times or that offer fall leaf color.

One of the attributes of mulching is that it discourages the germination of seeds (weeds, primarily) so you will get the best results from seed if they are sown in a clear area. Direct sowing of perennials may also not provide the best results - you may want to start them in seed trays indoors first and transplant to the garden when they develop some size. Or go with already started plants. Check out the Winter Sowing forum here on GW for lots of tips and helpful advice on starting plants from seed.