90 mins is plenty of time to connect in Doha. However the distances between gates can be extremely far and as such I recommend requesting assistance as others have suggested. My husband always requires assistance and Doha is remarkably helpful in that respect. On different occasions with very tight connections (although legal by Qatar standards) I have also used Al Maha services. On the occasion we used Al Maha service our incoming flight was late however they were able to expedite getting us to the gate at the last minute.

I have also booked an earlier flight into Doha if I'm concerned about the connection especially when going to a destination with limited service. Yes, I have a long layover and can get a hotel if I want, however it provides peace of mind especially when travelling with someone with limited mobility.