I was actually making a similar character. I decided on pure dfa with a strongheart halfling (Faerun players guide) with the glimmer skin template (Dragon Magic). But for you I'll suggest a few alternatives that would work. But first I'd like to discuss the difference between Dragon fire adepts and dragon shamans.

Dragon Fire adepts are nice if you want a breath weapon right off the back and invocations. They also get some nice breath affects which allow them to change the type of damage and affect their breath weapon does on top of their ability to do either a 30ft cone or 60ft line of fire. Their dragon kin ability is also cool alongside the bonus feat dragontouched which allows them to qualify for dragon heritage feats which are the bomb. Their scales are pretty cool too. The one downside that I can really find to them is that they cannot qualify for metabreath feats such as furious inhilation, since their breath weapon is at will instead of every few rounds. This is where Dragon shamans beat them hands down. The better HD and BA on DS are equal to the ability to use invocations. The DS auras are also nice for support to the other players. But the fact that DS's don't get their breath weapon till lvl 4 is kinda a downer (if you don't take into the affect that their breath weapon energy type and shape never changes). I see the appeal of both classes, and depending on the starting level of the campaign I would play either, but for level 1 I like DFA.

Now for you I would start off with a level of DFA, maybe take a few more levels in it till you get to the scales ability, then multi class into Monk or Battle Dancer. That would give you the unarmed combat ability you need. I'd honestly stay away from warlock or totemist for Natsu, but that's just me. The feat monastic training allows you to freely multiclass between monk and one other class, and perhaps going into the Martial Monk variant would be beneficial to you. Battle Dancer is nice with it's Cha based abilities, which ties into the DFA's invocations. BD come with some fancy maneuvering that could also aid you there. DFA's also get an ability at higher level that lets them use a targeted dispel magic to gain temp hit points, effectivily devouring magic.

DFA is one of my favorites for allowing characters to qualify for dragon hertiage feats, one of which gives you resistance to the energy type of the dragon you choose (for natsu red-fire of course) equal to 3x # of draconic feats you have. Also draconic skin which ups the scales ability of the DFA. Combine these with Draconic toughness for extra hp, senses for a bonus to spot and listen (as well as lowlight and darkvision) and power for a caster lvl boost and you're pretty much set. Combine that with the basically at will abilities of the Battle dancer and you've got a competant melee fighter with some fire power. Or take the Martial Monk variant and use the monk bonus feats to augment your unarmed strike.

These are my suggestions, but you're free to build it as you see fit.