Regarding updates - looking at the OnePlus CE 4 Lite, it gets 2 Android OS updates and 3 years of security patches. It was released June 2024. I read that as it gets security patches until June 2027. This seems to about normal. With some vendors patching more often than others. iPhones get far longer support. You are looking at something along the lines of 5 years with them. So with a cheap Android assume about 2 years. Older models are tempting as they are often on offer. But then you might only be looking at 1 year or expired security support. It's up to you if you want to ride bare back or not!
Some of your choice will be form factor. A large phone is fine for some, unwieldy for others. The benefit of a larger phone is sometimes a bigger battery. An Amoled display will have better contrast. And a large phone will probably be good if you watch video on your phone.
I'd rather the smallest phone available with a quality fast camera. I have no need to use the phone for anything but a little searching, the odd map use, the odd message and call. I'd rather use a tablet, laptop or something else to do the majority of my Internet stuff. Large phones are great, but I don't think I have a pocket big enough.
Regarding iOS vs Android, there isn't a lot in it. Especially if you turn on touch gestures in Android, they aren't that much different, and if you are vaguely tech savvy you could switch in a weekend. iOS will likely be more polished and generally better supported as Apple targets fewer devices.
If on the other hand you can only just about use what you already have, stick to what you have, and possibly keep the same manufacturer. Moto, Oneplus, Honor, Oppo, Xiaomi, Samsung all have different user interfaces - they are subtly different. Moto and Google phones are stripped down.
Newer Pixels get long term support from the 8 series, and have a good camera. We've an 8a in the house. I'd happily use that. I reckon they'll drop to around £200 again during black friday sales. Last years models usually do.
If you do use your phone lots, for surfing and multi-tasking, perhaps pick something with more memory than 4GB. The exception being a second hand iPhone 12, iOS seems to run smoother with less memory.
There's an Honor 200 lite for £142 on ebuyer.
A Green Moto G35 for £108 and Moto G55 for £147 at John Lewis.
Samsung A16 5G (silver) for £140 at John Lewis.
You might be able to pick up a second hand iPhone (don't bother with anything less that the iPhone 12) for under £200.
If you an infrequent phone user, just go for the Samsung as it gets plenty software support (6 years) and 2 years guarantee from JL. Perhaps send it back if you hate it! Or wait out for the sales.