Cusco to La Paz - where to see in between?

I have three nights spare/free on a solo holiday I'm taking to see Peru and Bolivia in October this year. I'm currently working out how best to use this time slot. I need to be in La Paz for the 13th October for another trip that is already booked to see the country, and I am leaving Cusco on the 10th October.

Visiting and going to Lake Titicaca by bus, is the most likely and I am thinking of going there for 2 to 3 nights (Puna is looking a likely spot), with some day trips from there, before moving on to La Paz. There is no flexibility in time frames and the budget is pretty good. Recommendations on how people have visited this area previously to use this time, day trips or services; and do so on the journey from Cusco to La Paz with the best places and trips in between those two, would be greatly appreciated. Companies used for travel would also be great. Thank you in advance.