If the cheaper the better you could:
Buy something like a used Dell Precision 7760 (with a graphics card) for about £700 off ebay. These are proper architecture mobile workstations, with proper over the top engineering. Be aware of the size and weight of such tank-like laptops.
Or you could put together a custom self built (or built by a friend) desktop PC for about £1000 depending on options, which you supplement with a 14" used premium business general purpose laptop (for under £200).
Look out for c£100 deals on large (like 32") used 4k monitors on ebay.
And look out for deals on used Wacom type architecture drawing tablets.
You should be able to get a new ergonomic mouse for about £20 from Facebook Marketplace or ebay.