Legal structure for your group
You have said that your organisation will have members, will be charitable, will be led by volunteers and will not be incorporated. A legal structure for you is:
Charitable unincorporated association
An unincorporated association is a group run by and for its members. Many community groups have this structure. It is quick and easy to set up. You just need to write and agree a constitution. To make sure you have legally charitable aims, its best to base this on the model provided by the Charity Commission. Charitable unincorporated associations must register with the Charity Commission if their income is above £5,000 per year.
Your route so far:
Voting members? Yes. Charitable? Yes. Paid workers in charge? No. Incorporated? No.