Luke, Jimmy n I have a 100k loop of Edinburgh that takes in pretty much all the quiet bits.
The busy bits can be dealt with by an early start. The loop can be cut short at any point easily too to make it shorter. It’s pretty good and mainly flat.
We start at fairmilehead, out through Morton hall, cross danderhall at the bypass, then on to musselburgh, head west along the coast all the way to dalmeny using paths and small roads, through dalmeny estate onto Queensferry, then cycle path up to kirkliston, ratho, back roads to Balerno, up back of Balerno to reservoirs (just doable on 23c…) Then passed my place, Colinton, back to Fairmilehead. You could sub sections out from Balerno and use WOL etc.
Anyway, I can map it for you and you can look at sections suitable for you and L-Unit.
M