If what they say is true, that the fight in the east will be an artilery duel, then with the 155s the Ukrainian have will out range the Russian.
Then the only concern would be to protect the 155 batteries from Russian aircrafts. So look to western made mid to high altitude SAM systems as the next step of escalation. The SAMs are also more useful in shooting down cruise missiles.
The Russians have a real problem with intelligence gathering; they don't seem to have the ability to gather live intelligence and act upon that information; hence they usually seem to target fixed installations, and on occasion, whatever mobile asset that hasn't relocated in enough time.
In addition, the Russian Air Force doesn't seem willing to risk their aircraft; the majority of the observed operations involve Russian Air Force strategic bombers lobbing missiles at Ukraine from well within Russian air space, and if Russian Air Force aircraft do cross into Ukraine to attack, they generally take safe targets for them such as Mariupol, where the Ukrainians have no air defence.
Even then, the Russian pilots remain skittish, preferring drop their payloads and then bugging out ASAP. They don't do any patrolling over Ukrainian territory at all it seems, no CAP (combat air patrol). This means that unless the Russians have a specific target they want to hit, Ukrainian forces can move around relatively well without fear of being discovered by Russian aircraft.
The problem is that the Russians are running out of long range missiles to conduct said attacks, and have no ability to replenish their stocks due to sanctions.
Finally, the Ukrainians have adopted shoot and scoot operations with their artillery, along with dispersed artillery support. When they shell a target, they do so from dispersed positions from all directions from a variety of guns and mortars, and due to the limits of Russian counter battery technology, the Russians can't effectively target every single position; their counter battery technology makes the assumption that enemy artillery is shooting from concentrated positions from one direction and stays there while they attack a position.
The Ukrainians have the technology and doctrine to shell Russian positions from dispersed locations from a variety of different types of guns and mortars of all sizes, dispersed across a large geographical area, and is capable of bringing them all together to shoot at a position with every round from every gun hitting at about the same time. Then, after each gun has fired a few rounds, the Ukrainians then bug out and go to another firing position, and repeat the process all over again.