In the region of D&D 3.5e Homebrew, there is the Slime Child (LA+2) Race. A modified version of this seems like your most desirable choice. Some highlights:
-2 Dexterity +4 Constitution, -4 Charisma, +2 Wisdom (could be simplified as +2 Con and Wisdom, -2 ChA)
Partial Ooze Traits: a Slime Child has many of the same traits as ooze creatures, including immunity to sleep effects, a Slime Child eats, but does not sleep and cannot wear heavy armor. But due to their human ancestry they are subject to paralysis, stunning, polymorph effects, and are subject to critical hits and flanking. They are also affected by any spell or effect that could target an Ooze.
Partial Human Traits: Slime Children are affected by all spells and affects that can target a humanoid despite being an Aberration. Its the result of a flaw in their initial creation process.
Slime Core (Ex): The slime child has a vital point and thus is vulnerable to critical hits and precision damage is extremely difficult to hit them and giving them a natural resistance to such attacks in the form of a 75% miss rate for critical hits and precision based damage such as from a sneak attack.
Favored Class: Fighter
A third party company, Alluria Publishing, made Squole, a sentient Ooze PC race (which would be easy to handwave as liquid). Among other things, they seem to have Blindsight 40ft. If that is an acceptable exchange, you may have to purchase the sourcebook because it's not SRD content. There's a Reddit review of it if you want a little more information before investing.