I'm in a similar boat. I currently have a Yoeleo M91 Ghost HT frame. Manufacture specs it out with a HA of 69.5 degrees and recommends a 100-120mm fork. I'm assuming this headtube angle is with 100mm(somebody please correct me if I'm wrong). My plan is to convert it to a 27.5+ bike with 120-130mm of travel. I want the HA to be around 68 degrees which I will adjust accordingly with a Angleset Headset once I figure out where I'm at with the conversion. I would love to see some slack HT's if anybody has seen any. What frames have you been looking at OP?