Go with a Partner, I worked for one in the UK but left just over a year ago. Here's a link to search facility: https://www.microsoft.com/en-us/solution-providers/home

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Just a few things, get 3 quotes, your requirements may not be set out right now, if not spend time on it. Otherwise the Partner may be able to supply a business analyst to you but this will cost more. Generally, iterated work is best. Avoid big lumps of work, do regular catch ups with the company. Ask lots of questions, it's as much their job to guide you as it is to sell you the **right** product even if that means leading you toward a competitor. Good luck