Another item useful in pressing - i.e. a wet cloth is a good old fashioned linen tea towel. Also pieces of cotton sheeting are good, so when your bed sheet has had it i.e. worn through in the middle, the edges of the sheet are still thick and so very useful.
Another pressing cloth that is useful is a piece of silk organza - a pricey piece of equipment, but you can see through this. Wool as in coating is wonderful in that you can do all sorts with this fabric, and it does respond well to a wet cloth and hot iron, and when setting the roll line on a tailored collar the heavier the iron the better, also with careful manipulation you can shrink what would have been darts out of a skirt, so no bulky darts around your middle.
With regards to Gimp - I was taught to use gimp and have one precious reel, have never found this since. However I believe that Empress Mills may do this, I haven't been on their website for a few years, but it is worth checking to see if they still do this.
I personally love corded buttonholes even on summerweight fabrics and I use DMC Perle thread mostly in white and I then close up the machine stitch and the white does not show through. The Perle thread comes in various sizes and either in skeins or a ball, and I tend to use No 5 and this gives a lovely buttonhole. Of course the skeins of DMC comes in lots of lovely colours, so you can easily get a matching Perle thread if you wanted to.