looking for a mod that gives unlimited bag space but not unlimited strength

While I know such a mod exists, I can't think of one off the top of my head.

I would suggest that you instead try a companion mod or a pack guar mod. This way, you have much more space for things as you can hand them off to the guar or companion, but you won't break your experience and make the game too easy.

http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=7428 allows for 50 times the normal encumbrance but not unlimited. Having a maximum of 25000 instead of 500 should be more than sufficient though.

If you are familiar with the CS it is easy enough to create a cheat feather item or tweak the GMST.

:)

You could use the "http://www.uesp.net/wiki/Morrowind:Glitches#Soul_Trap_Glitch" to give yourself a big feather spell.