Unfortunately there are no hand railings on the Field Level of AT&T Park. To find seats which do not require any stairs on the lower seating tier, you will need to be in the very last row at the the top of the section.

No hand railings as you look down the aisle between Section 110 and 109

As for the Upper Deck 300 Level seats, these sections feature hand railings in every section, but please take caution as the aisles on this seating deck are far steeper than down on the Field Level. With the entry tunnels located just above Row E, the best options up here will be Rows D-E where you will have a hand railing and do not need to walk up or down many steps.

Hand railings in Section 326 Row A