I haven't found any good ISA brokers that support stop loss. IG, T212, Freetrade forget them. Interactive Investor, is quite expensive but many go with them as they have ISA and SIPP. The only everyone is recommending is Interactive Brokers but they don't have ISA. I think if your serious in wanting to day trade start with IB and forget ISA and deal with the taxes later.Welcome to T2W.
I trade with a selection of brokers doing just that.
You shouldn't have any difficulty finding an established broker that suits your needs for day trading.
But best avoid the offerings from old guard fuddy-duddy high street banks if you want better charting and a reliable easy to use interface, unless you like being logged out every few minutes and having to verify every tiny transaction 'for your own protection' ha ha.
But seriously, there's a whole bunch to choose from, just check out any that undercut the 'old guard'.
It costs the broker just pennies to execute your trade, so any charging you pounds for doing so need to be offering very, VERY good support for overcharging you with high fees.
If you get really stuck finding one that suits, by all means message me, but you find one easily enough.