90 minutes between flights when you have to move bags yourself at AMS is very unlikely to work. Remember BA has a 60 minute checkin deadline at AMS.

I consider bag delivery at AMS to be reasonably good, in my opinion. I go there quite often and always check a bag, and I usually have to wait 5-10 minutes for my bag to come out after I arrive at the belt. However, I have a Privium (iris scan immigration pass) card, I walk quickly, and I know exactly what I am doing in Schiphol. However, because of the distances in the airport, I would still be quite surprised if I could get from my bum in the seat on a BA flight to in front of the BA checkin with my bag within 30 minutes. The slightest slip will doom you.

So, have a backup plan. Easyjet has many services to LGW at reasonable prices (even for a walk-up ticket) for a Plan C or Plan D. If you really want to try it on BA in 90 minutes, take C-W-S' advice about a Plus ticket and same day change.

FYI: BA usually uses baggage belt 4, if not 4 then 6. Very rarely any other.

FYI2: When you exit the Customs border after collecting you will need to go towards "Departures 3" for the BA checkin. Probably the easiest way to do that is actually to go towards baggage claim 15-22 (through a connecting corridor), then out through a customs exit (preferably near bag belt 16 or so), then immediately go up and when upstairs go to the right-most set of checkin desks (as you look at them from the top of the escalator) where you will find BA in check in desks 17 next to the Douwe Egberts coffee bar. If you're using Easyjet, they are also up there in the middle.

Look at the Schiphol map here to see the lay of the land: https://www.schiphol.nl/en/airport-maps/
Choose level 0 (bottom right selector) to see the baggage belt numbers, level 1 to see departures.