Lap infant vs buying a seat for long-haul (Australia) with 1-year-old — worth the extra $2.5k?

My wife and I are planning a 3-week trip from Denver to Australia to visit family (also our 10-year anniversary). We’ll be traveling with our baby who will be ~11 months on the way there and ~12 months on the way back.

We’re deciding between three options and would love real-world experiences from people who’ve done long-haul with a baby around this age:

Option 1: Lap infant (~$4,300 total)

• United both ways
• Would try for bulkhead + bassinet, but not guaranteed and may be tight on size
• Otherwise holding him most of the flight

Option 2: Own seat on Air Canada (~$6,800 total)

• Baby gets his own seat
• Air Canada allows inflatable bed extensions (specifically the Flyaway Kids Bed), so we’d have a full row setup for sleep

Option 3: Own seat on United (~$5,600 total)

• Baby gets his own seat
• Would attempt some kind of inflatable leg rest/bed situation, but less clear what’s actually allowed vs enforced

Price difference between cheapest and most expensive is about $2,500.

For those who’ve done 10+ hour flights with a ~1-year-old:

• How big of a difference did having a separate seat make?
• Did it meaningfully improve sleep (for baby and/or parents)?
• Anyone try the inflatable bed setups—worth it or overhyped?

Not looking for safety debates—just trying to understand the real comfort/stress tradeoffs on flights this long.

Appreciate any insight.