When I went to London in 2018 (two separate trips there that year), I found that many sights, including most of the ones you listed, had a discount for booking online in advance. What I figured out was, except for places that needed a timed ticket like the Churchill War Rooms, the morning of my visit was far enough "in advance" to buy the ticket at a discount.
So, look at the websites of the places you're interested in. If there is a discount for an advance ticket, create an account now from home (much easier on a desktop computer than on your phone!). When in London, if you decide you want to go to the sight, just log in on your phone and buy the ticket that morning. Check if the sight will scan the ticket off your phone, or if you need it printed out before you arrive; if the latter, see if your hotel will do it, or if not, allow some time to get the e-mail confirmation converted to a paper ticket at the sight. At least when I went, some sights did not accept tickets on phones, but this is the kind of thing that changes.