I don't know if 3.0 material is allowed, but Masters of the Wild had a Shifter PrC that had a 10 level Greater Wild Shape class ability progression.
This allowed for the addition of other types of creatures: (1-Humanoid, 2-Animal, Monstrous Humanoid, 3-Beast, Plant, 4-Giant, Vermin, 5-Magical Beast, 6-Aberration, Ooze, 7-Dragon, 8-Undead, Construct, 9-Elemental, Outsider)
...and various size progressions: (1-Small, Medium, 3-Large, Tiny, 5-Diminutive, 7-Huge, 10-Gargantuan).
...and other class abilities.
No spell progression. Not required to be a Druid to enter, but it helps.
...I feel silly now. Indeed it is.Master of Many Forms IS the 3.5 update to Shifter, the book even says so directly.
Just one thing to say on OP: Never ever EVER EVER E V E R give up your casting.
For another idea, you can get monk attack progression plus natural attacks. Giving up spells for monk's unarmed strike seems fair trade to me.
Or you can make barbarian/fist of the forest/bear warrior/warshaper instead of druid. Sure it is only bear you turn into, but it is NINJA bear lol. And if you are dwarf throw in deep warden lvls to get 2xCON mod to AC.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.