A synonym for "soft" with a negative connotation
Solution 1:
How about delicate? Mealy-mouthed (from @Josh61 's answer) conveys what you want more precisely, but delicate has that soft negative connotation.
fragile; easily damaged; frail. From dictionary.com
An alternative if you don't like delicate could be squeamish:
easily nauseated or disgusted. From dictionary.com
Solution 2:
"tender" has the connotation of being gentle and soft.
"Oh, you French people are so tender, just say that you're looking for something to kill the mouse with."
- tender (adj) marked by, responding to, or expressing the softer emotions, showing care.
Solution 3:
One of the senses of precious may work:
- Affectedly dainty or overrefined: precious mannerisms.
{AHDEL}
though this obviously covers an affected attitude.
If the person is genuinely soft, the dialect term nesh would often be used conversationally in the UK:
nesh adjective
dialect
(Especially of a person) weak and delicate; feeble
{ODO}