UK—charity shops

Every year I probably donate and buy ~£150 worth of stuff in charity shops. At the moment I try and do this mostly via Oxfam, because TLYCS thinks they’re decent, they have shops everywhere, and putting GiftAid on donations is easy once you’ve set up an account. In the past this number has been quite a bit higher, maybe like £300, and plausibly could go up again

Other shops that I see a lot like Cancer Research UK or British Heart Foundation seem likely to be a lot less effective.

The amount of money involved makes me feel like spending a lot of time thinking about this isn’t really worth it. But I wondered if I’m missing something obvious. Are there more effective charities that run shops in the UK, or some other way I can donate items to more effective charities? For higher ticket items I sometimes sell on eBay as you can donate the proceeds directly to a charity, saving fees and potentially increasing awareness of say AMF to whoever buys the thing. But for a pile of not valuable paperbacks or something this doesn’t always seem worth the time