Large 1st Class (£1.06) made up of three stamp combinations, with mixed designs e.g. 65p + 23p + 18p etc. Using three stamps will give you additional savings. The majority of these stamps only come with lick and stick gum. This is the Royal Mail's new rate from 25th March 2019.
£1.06 is quite an awkward rate to make up from existing stamps so it may prove difficult to source sufficient stocks to meet demand.