Found a champagne cork in the work pantry (probably from an afterwork drinks sometime ago) which I cut and measured up as I went along, test fitting until I got my preferred loft. Used a UHU type glue to set. With the knot and the cork it still added noticeable weight but I think it’s just relative to its small size in the first place.I might have missed it, been offline for a bit, but how did you end up fitting the knot?
The cork is a good alternative to washers as I could cut to size and not waste glue filling holes like with washers.