Thanks for all the comments. I’ve ordered my uPVC sash windows from the manufacturer. They don’t do the fitting themselves, only recommend local contractors, but the quotes I’ve had are quite high. I’m tempted to try installing them myself to save some money.
I’ve seen a fair few people talking about DIY windows installs. Some say it’s straightforward, others say it’s a nightmare. If you’ve ever tried fitting your own windows, how did it go? Was it worth it, or would you call in a pro next time?