There are a few combinations of adapters I use to reach focus depending on no barlow or barlow. With no Barlow, screwing the camera onto the eyepiece holder sets it too far back. You need to unscrew the eyepiece holder and screw on an adapter that's about half the length of the eyepiece holder. I have this, but there may be cheaper versions:
As an alternative, you can remove the eyepiece holder, screw the camera directly onto the diagonal, and then slide the diagonal further back out of the telescope, again about the same distance as half the eyepiece holder. This works fine, just less solid of a connection with the diagonal slipped out a bit.
With barlows, I have not been able to directly connect them to camera. I chose barlows that the front 1 1/4" barlow element can unscew from it's eyepiece holder. For these I leave the diagonal eyepiece holder in place, drop the unbscrewed barlow element down the eyepiece holder, and then screw the camera directly on the eyepiece holder.
This barlow works but when dropped down the eyepiece holder give about 1.6x instead of 2x.
And this one works using same method, but give 2.2x instead of 3x.
Hope you find all this helpful and feel free to ask any other questions. I'm relatively new at this too, and have had great support from folks here. I'll add this info to your post in the forum too, in case others are looking for similar answers.