OP, at some stage answer questions I asked in earlier post.
Then folk can advise correctly.
There is no retirement visa.
You will be obtaining a Non O based on retirement.
This provides a 90 day stamp then you obtain subsequent extensions.
You can obtain a Non O from a visa exempt or tourist visa entry.
Read this thread and the links
https://aseannow.com/topic/1311886-visa-exempt-to-retirement-extension-process-and-cost/
You mention EU. At a guess your embassy will provide "income letter"(not UK) and you could use income method.
Non O cost 2000b
12 month extension cost 1900b