Silk would be good, however it really depends on whether it matches the mill who've woven your wool tartan and how that matches up. I'd get a swatch of it and see if it looks like your tartan.
My Campbell Ancient kilt was woven by House of Edgar. I believe Lochcarron make a silk version of the tartan and you'd never guess it was the same tartan. The greens a different shade, the blue's almost a whole different tone and the sett is half the size.