for churches + yards look at manxnotebook
there are several yards a resident of Douglas could be in - Braddan Old (pre approx 1860), Braddan new (post 1848), Douglas Borough old + new(post 2000 + crematorium) + St Georges in Douglas + Onchan for North Douglas

books of MI's are sold by IoMFHSoc - for 19th C yards + older yards post the 1882? burial act there will be records of grave use - previous to this your family dug your grave or arranged for it to be dug - only record would be a MI

Go to Manx museum - all books of MI's are there to consult + staff are very helpful - they also have original records for some yards.