First replacing the door is challenging, but doable . Doors come in even sizes 30" , 32" 36" are standards . Bedrooms are usually 30 - 32" and are 1/38 thick.

yours may measure oddly depending on original conditions . But a replacement will be close to standard sizes.

Buying the new door . Your local Home Depot has a good selection of doors . You can buy a blank door (no prep) or a pre-fit door with the knob cut out and cut to size basically 3/16 under the original standard size this is the one I recommend if you don't have the tools to start from scratch.

Doors are right handed and left handed so just make sure the one you get (pre-fitted) has the knob on the correct side and is pre beveled. Only thing you "should" have to add is the new hinges.

Installation , remove the old door by driving the door pins up and out. Leave the jamb hinge half on for now.

remove the hinges from the old door and save them (important u save them) . Now a test run of new door without doing anything place the new door in the opening and see how it looks , if Alls well, we can add the hinges . Note: the knob may be off a little so you might have to adjust the strike on the jamb.