New building design

I'm looking into a setup for my company for a new building and I'm looking at the switching.

My current setup is 2 "core" switches acting as the layer 3 gateway for all VLANs (odd number 3rd octets are primary on Core1 and evens are on Core2) but each access switch has one 1 connection to a core switch. I use Juniper wherever I can. Currently I have 2x EX4200 for the core switches and a mixture of 4200s and 2200s for the access layer.

I have no issues with bandwidth, but I'm concerned with resilience. Currently it's a massive pain to update the OS on either core switch as it takes out half the building (gateways fail over using VRRP, but as each access switch only has 1 connection I lose half my switches).

I could use spanning tree to go from the edges to both cores, but it feels like a dirty way of doing things.

Is there a way to run layer 3 to the access switches, but have layer 2 adjacency between different access switches? e.g. a port on Access1 can be in VLAN3 and a port on Access2 can be in VLAN3 and they can communicate as if they were on the same switch on the same subnet?

My initial reading brings up L2VPN with MPLS, but this feels overkill.

Is what I want to do a good idea? Is there a better way of achieving multiple uplinks to 2 core switches?