If further maths wasn't 'doable' it wouldn't be an A-level course. So yes. And also the majority of people who take Further Maths have no experience in mathematics other than GCSE, so you are not at any major disadvantage.
That being said, Further Maths is by no means an easy subject. It is more difficult than single mathematics and requires a lot of temporal investment for the same output in comparison with other subjects. Do not think that getting an 8 or 9 at GCSE means you are set for an A or A* in Further Maths. GCSE maths and A-level Further are in two completely different leagues. You are no longer competing against a whole cohort of teenagers who begrudging sit GCSE maths and aim to scrape a pass - you are competing against those who are set on doing mathematical courses at uni and are fighting to meet uni grade requirements.
Take this into consideration. I think for your course specifically taking FM would be a significant asset, but do not take it unless you are willing to put a lot of time into it (far more than for GCSE maths).