Hello, I am risking an usual question but any direction

Hello, I am risking an usual question but any direction may help.

Is there any retired British person in my situation here, living and full time resident in Italy.? I have a quick question.  In a few years time  I will retire and try to aggregate a tiny Italian state pension with my UK state pension (towards which I currently pay class 2 voluntary contributions). That's one thing. In addition,  I will have a small UK private pension and a small UN pension.  My question is, do I have to declare the private pension at some point and same thing with the UN pension? (I know people, some of them Italian., who receive a UN pension and do not declare it , this is because the UN salaries are not taxable by Italy in the first place)

Last, if you are retired and resident in Italy, and have a similar "complicated" situation, what do you use to do your tax declaration in Italy? Any advice welcome

Thank you