First thing's first. The costumes can be as high or low brow as you like. Around the office, we have a lot of different ideas. There are fans who are deeply dedicated to period detail, and they're looking into renting from a theater company. ( We did say deeply devoted, right?)
For those of us who are slightly less dedicated, we're looking to local costume shops to see what's available, popping into flea markets to see what we might be able to own (instead of rent for just an evening) and visiting local department stores and thrift stores to see what we can see. After all, why not take a good deal when you can find it?
Also, while I haven't heard of anyone brave enough to attempt it (and as a novice seamstress, I consider attempting something like this the epitome of bravery), there are also patterns to be had.
With two weeks 'til party night and Christmas coming up, however, I see myself as closer to the potential for being one-ripped-seam-away-from-a-nervous-breakdown than being capable of stitching together my own "Downton Abbey" digs. I'll gladly pay homage to those of you who are ready to pull it off, though!
More along the lines appropriate for my tapped-out brain and mid-level DIY skills, however, are these great fascinator options! They are very, very Downton Abbey-esque, since Lady Mary's love for hats has proven far less capricious than her love for Cousin Matthew (in my humble opinion). And who can resist an excuse to wear a good hat?
Here are a few ideas for inspiration (or ownership, if you'd like to purchase tutorials or the hats themselves):