Have you looked at the KS2 Cavern Assortment Pack? That is how they are selling the KS2 stretch goal pack. It looks like it is currently available in the store unpainted.
https://shop.dwarvenforge.com/collectio ... -unpainted
The assortment pack, in addition to a variety of walls and floors, gives you four chasm pieces (ledges), a couple of narrow passages, a couple of 45 degree angle passages, and some free standing walls. I am also fond of the spider web.
I didn't know about DF until KS3. So... when I was back filling my collection, I found a couple of the assortment sets gave me quite a variety of pieces that minimized additional purchases... Your needs will be different since you have KS6 to consider. It will cover some of these items such as free standing walls and ledges (from the trifecta pieces).
Just something else to consider for the variety of additional functional pieces you could have now rather than in a year.