It is hard to say without seeing any images. If it is only a moisture problem, then I would say no, you do not need a sump pump. Just ensure that there is a steady supply of air passing through the crawl space to ensure the area stays ventilated and that excesse moisture is carried away. To do that, ensure your air bricks are clear or install additional air bricks.
If however, you are having a regular issue with puddles and excess amounts of water building up under your property, then yes, I would suggest consider a sump pump as the excess mositure could lead to addtional property problems such as wet or dry rot. However, before considering a sump pump, it may be an idea to consider how the water/mositure is getting there in the first place. Is it because the water management systems within the property are defective and need a little TLC. Is it because of the lay of the land and you need to install a drainage channel on the outside of the property to divert excess amounts of water? Could it be because of defective plumbing?
Before doing anything, I would strongly suggest contacting a few other companies for help and advice. Make sure you also check their credentials and whether they are a part of any professional bodies.
I hope the information helps and I hope you do not mind, but I have included a link to our sump pump range with a video comparing sump pumps and what you should look out for when enquiring about a quality sump pump.