If a picture is worth a thousand words, then I just saved myself some typing with this screenshot :)
What to avoid:
Repeats: Monthly Repeat Every: 12 months
Repeats by: day of the week
There is a bit on Wikipedia about timezone adjustments relevant to Summer times here.
The above screenshot is from a Cloud service calendar (Google), and similar repetition settings can be achieved in a free software calendar also:
By selecting 'Custom' in Thunderbird calendar, you are able to select 'The Last' - precisely what you need for a reminder set to Last Sunday of March.
Thunderbird is cross platform and available for download at