I'm a bit afraid of opening my own company. I have a great idea but it's hardly revolutionary. I'd rather not spend loads of money on lawyers or go broke early on if a patent already exists for my product, but I'm not sure how I can protect myself.
What steps can I take to stay safe from patent trolls, and does it matter what country I'm based in? Could I, for example, be sued in the UK for unintentionally infringing a US patent?
Understanding and protecting your intellectual property (patents and copyrights) is one of the most important early stage responsibilities of the founders. You simply must find respectable legal counsel to assure you idea can be pursued. If it is a violation of someone else's IP then it is good to know early and save the time and money of a start up. If your ideas are unique, it is critically important to get them protected. It is not over the top expensive to do a patent search and to file provisional patents for protection. I believe you have one year to move forward after filing a provisional patent to work on the filings to completely protect your ideas. Please contact respected legal counsel in your area. This is very, very important.
It sounds like you plan to use someone else's IP for your product, not that you are trying to protect your own IP. To your last question about "sued in the UK for...infringing a patent in the US": intention does not matter but location does. If you sell your infringing product in an area that is covered by a patent, the patent owner can take steps to protect her patent. If you sell and ship your infringing product only in an area that is not covered by the patent, you will probably be safe.
I recommend that you use patents.google.com and do several keyword searches to see what is out there. it is much easier to use than the USPTO.gov site.
You might call the patent owner a "troll", but that is also not relevant. A patent owner is entitled to protect her interest. However, the NCSL reports that some states are trying to take steps to reduce the impact of trolls. http://bit.ly/2k9959B