I'm trying to book (with accompanying adults) an "infant in seat" ticket on LY. But their website only shows passenger types:

Children (in the main dropdown) -- which I assume is a child fare for age 2-12

and

Infant (0-2) -- which I assume is a lap infant

because it seems to be pricing that way.

How do I force it to book an Infant in Seat ticket? Can this even be done online?

Also, it's hard to see from El Al's own site what exact booking codes their Economy "fare types" really are. Any way to find that out?

An example fare breakdown that I want from ITA Matrix is:

Fare for 1 infant in seat
Fare 1: Carrier LY WUKRT7 LON to TLV GBP83.45
Passenger type INS, round trip fare, booking code W
Covers LHR-TLV (Economy)
Fare 2: Carrier LY URTUK TLV to LON GBP96.88
Passenger type INS, round trip fare, booking code U
Covers TLV-LHR (Economy)
Israeli Security and Insurance Surcharge (AP) GBP11.20
United Kingdom Passenger Service Charge (UB) GBP41.65
Subtotal per passenger GBP232.85
Number of passengers x1
Subtotal for 1 infant in seat GBP232.85