How bout going whole-hog Paleolithic? If you're not daunted by a total of about 3000 pages, Jean M. Auel's "Earth's Children" series is PHENOMENAL. 30 years in the making, research that took her to cave sites and museums all over Europe, a bout of cancer = 6 amazing books about an admittedly fantastical heroine in the midst of the Wurm Glaciation 30,000 years ago. Her most recent and final volume, "The Land of Painted Caves" just came out at the end of March. I haven't read it, but I'm DYING TO!http://www.jeanauel.com/books.php
Ahem, let me collect my composure here... It's the number-one compendium of European Paleolithic cultural information. Some of the conjecture she used as a basis for various things in the older volumes has since been proven sketchy or even false, but I'm sure that the same will be said for various information contained in the newer volumes (she claims creative licence for a LOT of interesting things). That said, it took four years to write the first novel, "The Clan of the Cave Bear." Auel is HARDCORE about her research.
For practical stuff like weapons and musical instruments, check out PaleoPlanet:http://paleoplanet69529.yuku.com/
Not much about clothing, but LOTS about every primitive skill you could ever hope to master
Aside from all that, I can make some suggestions that are realistic and not corny in the least. Depending on how you go about this, you can still be gorgeous and alluring, and entirely convincing. Alot of these suggestions are from Auel's work, but I also studied anthropology with a special interest in ancestral ('primitive') cultures.
Use natural coloured suede hides (browns, reds, oranges, tans), either just one colour or patchworked with different colours in a geometric pattern of some sort to make a dress. The style and shape are up to your personal preference, eg one shoulder, square neck, boat neck, pointed hem, rounded hem, asymmetric hem, etc. If you patchwork, you get bonus points for making the shades and shapes create a figure of some sort, like an animal that is special to you (must be subtle enough that only the most discerning and observant will notice it). Use artificial sinew or natural coloured upholstery thread for sewing. You need to overlap the edges of the hides, not do a "traditional" seam. Make your dress tighter than you think it should be but still loose enough you can bend over and move. The dress has to be tight because you're going to spend a few days breaking it in so it's comfortable at the party. Just wear it around the house and it'll stretch and shape to fit you.
Get some fringe action going, either as a long fringed belt, or make the dress floor length and fringe it up to your thighs. You could even make an armband of leather that is fringed.
Wear lots of jewellery made with natural materials, like shell, bone, and stone beads. Using sisal twine to macrame a couple of bracelets is a very good idea
You'll want an amulet or large pendant that is supposed to be symbolic of something important. A headband and strings of beads braided into your hair are possibilities. Don't use metal anything if you can help it. Don't be afraid to apply beads right to your dress in a geometric pattern or to complement your patchwork. If you keep the dress simple, a beaded collar covering most of the chest will give the impression that you're a wealthy woman who's extended family lives in comfort. Same with jewellery: the more ornate your jewellery is, the wealthier you are, because you have time to sit around making all this or have enough to trade with the people who made it, (a principle borne out in 'primitive' societies the entire world over).http://bohemiansoul.com/products-page/what-sold/sold8/
(there's some amazing stuff here!)http://www.etsy.com/transaction/29808741
Red is known to have been a sacred colour, thought by most to represent fertility and the bounty of the Earth. Paleolithic burials often have powdered red ochre on the bodies, and Auel uses the suggestion that it is symbolic of being reborn into the next life, covered in your Earth-mother's fluids. You'll want to use red in some small but significant way, such as a bone talisman rubbed with red colouring, or a bloodstone or jasper bead as the focal point of some piece of jewellery.
Centre-seam moccasins are very similar to footwear found during the Neolithic in Europe.http://www.nativetech.org/clothing/moccasin/mocinstr.html
That's about all I can think of for now. I hope that was helpful, and I'm so looking forward to seeing your finished costume!