So you are looking at either the ubiquitous 7xN type lathe and XX 180 type lathes, which weigh in at 60Kg or less to suit your requirement, which is as good as any place to start.
Others you can consider which are less commonly available include the SEIG products C0 and C1, I think they are difficult to get in this country now, in anycase the C0 may suit but is rather limited, the C1 much better (I may be biased because I have a C1 and apart from drive belt issues (easily sorted) it has never disappointed and can be manhandled easily.
Proxon, are available but rather overpriced (IMHO), and only the larger one has a leadscrew, I think. lathe.
Pultra is a plain turning lathe (no leadscrew) OK for clockwork if that is your bag, but it is very hard to find one that does’t need reconditioning at a sensible price. It is primarily a collet lathe and collets or any other parts and accessories are scarcer than hens teeth and priced accordingly.
Taig is OK, but again no leadscrew and very much a DIY project to motorise, but there is some back up via rotagrip. People do manage to do heroic stuff with these machines, despite it being a very basic offer.
On the ‘any old iron’ market you have Emco Unimats (best bet a Unimat 3 which is the lathe the Seig 0 is based on). Compact 5 is OK and can probably be lifted, (check on lathes.co). There is another Emco? with a half round bed that come up from time to time – cant recall at present.
You could consider a Myford ML10, pretty compact, a little heavier to lift at 65-70 Kg, but I managed to lug one upstairs by removing the motor and any other bits that could be easily refitted (I qualify as yer actual 7 stone weakling and regularly get sand kicked into my face, for the avoidance of those who might think I am one of those individuals who claim to be able to pick up an ML7 in one hand). The advantage of this lathe is there is a thriving secondary market in parts and tooling due to the ubiquity of its big brother, the ML7. These can be had at modest cost and are solid if quirky performers (but I may be biased).
Cowells lathes are still manufactured and come onto the second hand market from time to time, not used one myself but everybody else rants and raves about them (an so they should at the price).
Boxford/Emco 8s a bit heavy I think.
Wouldn’t bother with any other old Britiron, unless it in immaculate condition and comes fully loaded with chucks, tooling, accessories and sundries etc, otherwise you are in a world of pain and frustration trying to find parts, backplates unless you are prepared to fabricate everything yourself (and usually they are knackered anyway).
Probably loads of others, but thats my tuppence worth.