Five classes stand out to me as ideal choices for entry to warshaper.
Pugilist is a variant fighter from Dragon vol. 310. It gains Improved Unarmed Strike, slightly increased unarmed strike damage (but it doesn’t scale like the monk’s), the Endurance feat, and then one other feat (or special “Pugilist ability”) of your choice from a decent-size list (comparable to the size of the core fighter bonus feat list, but much smaller when you consider all of the supplement feats that a fighter can usually take). It’s kind of solid for all the feats you get in one level, but I’d definitely not take more than the one.
Pugilists give up martial weapon proficiency, but retain all armor proficiencies.
Knight gets d12 HD, heavy armor, and Bulwark of Defense and Test of Mettle in the first four levels. You also get the Fighting Challenge, which is OK, and Mounted Combat, which... is maybe useful? Anyway, the first four levels are pretty good (in fact, it is often claimed that knight has five good levels: 1, 2, 3, 4, and 20).
I would only go with knight if I got at least three levels; Bulwark of Defense is a really nice feature. I’d want Test of Mettle if my Charisma was good, but a level of pugilist or crusader could fit in well.
The big problem with knight is the Knight’s Code, which is possibly even stricter than the paladin’s (though the penalty is less severe). It also demands that you remain lawful: that makes it hard to also take a level of barbarian, and you want a level of barbarian, because...
Barbarians can get Improved Unarmed Strike as a bonus feat, but it’s not worth it to do so. Instead, you want a level of barbarian for relevant stat bonuses, d12 HD, and most importantly, the lion spiritual totem from Complete Champion. Pounce gives you absolutely critical mobility.
Warblade gets medium armor proficiency, not heavy, but also gets d12 HD, and a number of really useful maneuvers. Tiger Claw can let you attack more often, which is nice, with wolf fang strike and sudden leap.
Doesn’t get Tiger Claw like warblade does, and only a d10 HD, but it does get heavy armor proficiency, and more importantly, Devoted Spirit is solid, reliable non-magical healing. Crusaders are the best in-combat healers in the game, while remaining solid martial forces in their own right. Plus Steely Resolve can dramatically improve your ability to remain standing.
Crusader 4 itself could be a solid entry to warshaper, though I’d probably go with levels of barbarian and pugilist first.
Superior Unarmed Strike
This feat from Tome of Battle gives you a scaling unarmed strike damage similar to (slower than) the monk, if you care. It’s decent enough, particularly when you’re getting size bonuses.
Improved Natural Attack (unarmed strike)
It’s a damage boost that stacks with everything; might as well.
Note that in theory you could replace this with a fanged ring if you were in a game where you could expect to get a 10,000 gp magic item any time soon, but you aren’t
Another feat from Tome of Battle, this allows you to take attack penalties (similar to Combat Expertise, no larger than your BAB or 5, whichever is less), gaining a number of temporary hit points equal to twice the penalty. The temporary hit points last 1 round, but you can continuously add up to 10 HP that basically “doesn’t count” as damage you take ever round. At low levels, that removes a lot of damage.
Barbarian 1/Pugilist 1/Crusader 2
Heavy armor, a d12 HD and three d10s. Rage and pounce from barbarian, Improved Unarmed Strike, Endurance, and another feat of choice from pugilist, Steely Resolve, Furious Counterstrike, and Indomitable Soul, along with a bunch of maneuvers, from crusader.
For maneuvers, you get five 1st-level maneuvers, a 1st-level stance, and one 2nd-level maneuver. The crusader awkwardly only has only six 1st-level maneuvers to pick from, and leading the attack and vanguard strike are very-nearly identical anyway, so your choices in 1st-level maneuvers don’t matter that much. Anyway, vanguard strike is slightly better than leading the attack, and you don’t need both, so I’ leave out leading the attack and get the other five. For stance, martial spirit and iron guard’s glare pretty much are your best options; the former gives you more healing, while the latter draws attacks towards you by improving allies’ AC without improving yours. The 2nd-level maneuver basically should be mountain hammer, hands down.
For feats, Improved Natural Attack (unarmed strike) and Stone Power are my picks. From pugilist, probably Improved Initiative, since the list is pretty weak; Two-Weapon Fighting or Combat Expertise might be worthwhile if you want to go the TWF route or the tripping route. I’d probably get Superior Unarmed Strike at 6th (unless going for Improved Trip), and Snap Kick (also Tome of Battle) at 9th.