The stuff that will blunt the Russian advance - both tactically and on operational/societal terms - is stuff that isn't manpower intensive over what they already have in those roles, so air defence, air power, deep fires, CS artillery. You could increase both Ukrainian socks and their rate of use exponentially without requiring much in the way of force generation.
If the Russian Army in the field was under sufficient - and quite achievable - artillery and air attack, as well as having it's own logistics subject to air and deep fires interdiction, then the current Ukrainian Army is perfectly capable of preventing them moving any further into Ukraine, and indeed rolling them back as their logistical position becomes more difficult. This village, then that village, then this crossroads, rather than Blitzkrieg.
It's still perfectly winnable for Ukraine, but that depends on a) a fairly quick uplift on stuff they can use now, and b) the Russians seeing, and believing, that Europe will build, and finance, the munitions production that Ukraine needs for however long Ukraine's population want to continue fighting.
It will, obviously, cost the Ukrainians a lot more blood and wrecked cities than it would had this stuff been done in 2020, or 2020, or 2018, or 2023...