Sounds like folks have presented good options
I put an ETX -60 MM Meade refractor piggyback onto my Dob.
Used a triple shoe mounting bracket.
1) GLP to get you close. (GLP is out of view - mounted on the back side)
2) 9 x 50 raci - for exact centering and for a five degree FOV
3) and the 60 x 300 Meade for a 2+ degree FOV -( the 60MM FOV can be changed as you can change EP )
The 60 MM was just under 3 pounds.
It did require about 7-8 pounds of counterweight to balance the DOB
Nice to have a wide FOV option for every object, with the ability to change EP.