Best sales order processing software?

My client has asked me to choose and implement an SOP system covering sales and purchase order processing, stock and warehouse management, bills of materials, sales invoicing & financials etc. Audit trail from quotation through to invoicing is a must.

Small company, t/o £1.5m increasing to £3m in 2 years.

About 5 - 10 users

Not a full manufacturing coy, just component assembly into finished product. 

Sales to customers all over world.

Can anyone share their knowledge/experience/recommendation please?

Many thanks in advance.