It's certainly possible, but you need to take total responsibility for your own learning and understand when (and how) to seek assistance when you get stuck, if necessary.
In Year 12 I successfully self-studied Edexcel C1-C4, S1, S3, S4, M1, M4, M5, D1 and D2, with the bulk of the work taking place during the Year 11 summer holidays and during the various 1 or 2-week breaks scattered throughout the year. (FP1-3, S2, M2 and M3 were done in class.) It was the workload itself that I found trickiest: it's one thing to get A grades in those modules, but it's quite another to consistently maintain 90%+, so you need to make sure that you allocate as much of your time as possible towards doing as many of the textbook questions as you possibly can, including all possible exam questions, ensuring that you fully understand all of the steps involved in those calculations. In my opinion, the summer holidays after Year 11 and Year 12 are incredibly useful, because they really allow you to hit the ground running during term time: you don't necessarily need to go all out doing exam papers and the like during this time, but it is feasible that you could learn the bulk of your course content if you put in a few hours each day.
I don't know if Edexcel still do this, but they used to have an online 'solution bank' where they provided detailed solutions to all of their textbook questions. If you have access to a library containing the legacy textbooks (called 'Heinemann Modular Mathematics for Edexcel AS and A-Level'
, then borrow them -- some of the newer textbooks do take questions from there, but you'll find a few hidden gems of difficult questions in there, which I found particularly useful for Mechanics. (These were designed with the 2000 specifications in mind, so they're pretty old, but for general interest, you can find the old textbooks for S5, S6 and M6, which haven't had exam papers for something like 13 years, but are interesting reads nonetheless. (As I recall, S5 contains some stuff on generating functions which are quite useful if you plan to do any probability and stats at uni.) Here's an example M6 paper from back in the day:
https://papers.xtremepapers.xyz/Edexcel/Advanced%20Level/Maths/2005-Jun/23_M6_June_2005.pdfOther resources include the Solomon papers, which as I recall were 'harder' versions of the Edexcel papers, so these are great if you're running out of prep material, and I believe there are a few other versions like this ('Zig-Zag' might have been another, and one other brand whose name I can't quite remember).
I'd also recommend my own YouTube channel,
CrystalMath, for some integration examples and some stuff that might be relevant to the complex numbers topics in the Further Pure spec.