Looks good so far, except that the tripod will only reach up 4 feet.

Dug out my stock of tripods and I can gain about another foot, but I want
a line even higher up the wall.

So now trying to work out what I can position opposite the wall which is
tall enough AND broad enough to support the tripod so I can get the line
where I want it.

The usual process is to use the laser line as a datum line and measure up from it to the height required. If you repeat the measurement in two places then you can use use a chalk line to get a continuous line at the height you need.

Richard