[SalesForce] Lead status visibility

I know you said no validation rules in your question, but based on your comments it seems like it's more of the aesthetics that's keeping you away from them. From personal experience, as long as you have a good error explanation that doesn't leave users confused, they have no problem with validation rules. In case you decide to go this route, here's a rule that may work for you.

AND($Profile.Name = 'Read-Only Profile', ISCHANGED(Lead_Status))

Error Message: Lead Status is a read-only field for users with the profile 'Read-Only Profile'

Hope this helps if you decide to use this.

Workflows, Validation Rules and Before triggers fire on Lead Conversion only if the Setup > Customise > Leads > Settings > Enable validations and triggers is checked.

It might be worth checking if this setting is enabled, because otherwise the Lead Status value will not be synced to your custom field on Lead Conversion via workflow, and therefore not be copied across.

(Even then, I believe the Lead Triggers / Workflows fire after the Account and Contact ones, so it may be to late for the Lead Status to copy across)

The order of execution at Lead Conversion has been answered here

This can be achieved by a trivial LeadAfter trigger, or if the Lead Status is always set to Qualified upon Conversion, then you could set 'Qualified' as the Default Value on the Contact Lead Status field.

(One way of doing it also may be to only allow 'Qualified' Leads to be Converted - this can be controlled by having a different layout for Qualified Leads, when the status changes to Qualified, a workflow fires - changes RecordType to QualifiedLead and therefore associated Page Layout changes, which now has the Convert Button. With this approach, the Lead Status at conversion is available in advance and available to be copied across at Lead Conversion)