Hi,
I specialise in fully fitted bathrooms, wetrooms etc and I have found over the years that fitting cheap showers can generally be false economy, poor quality fittings, check valves and thermostatic cartridges that fail after a short time.
You can go expensive, Grohe for example, buy in my opinion and experience bar mixer shower valves, as in the picture in the other post, in the £70.00 to £120.00 generally offer the best between value and reliability/performance.
Screwfix sell two that i use regularly, one from Triton (on offer now at under £60.00) and another marketed as Swirl (two at £63.99 & £68.49). Others too in the £70 to £120 range.
Also Wickes do a slimline high density foam tray 760 x 760 x 45 for just over £30.00, set on silicone or expanding foam, but weigh the tray down, evenly, if using foam.
There are companies that offer a bespoke service for shower enclosures and doors. Not cheap but useful if height or roof shape is a problem, any plumbers merchant will be able to advise and get quotes for this service.
Hope this is useful.
Cheers
Don