Can someone point me to a commentary which discusses sakkāya -diṭṭhi?
Though you asked for sakkāyadiṭṭhi, I assume you are looking for sakkāya and then sakkāyadiṭṭhi.
So I gave references accordingly so you can quickly find the answers to both.
1.VisuddhiMagga Atthakatha
ñāṇadassanavisuddhiniddesavaṇṇanā,
pariññādippabhedakathāvaṇṇanā
Line of interest : sati vijjamāne khandhapañcakasaṅkhāte kāye, sayaṃ vā tattha sati diṭṭhi sakkāyadiṭṭhi
Stress is on : both sakkāya and sakkāyadiṭṭhi
2.Abhidhamma-Dhammasangani Atthakatha
Nikkhepakaṇḍo
Tikanikkhepakathā
Line of interest : sati khandhapañcakasaṅkhāte kāye; sayaṃ vā satī tasmiṃ kāye diṭṭhīti ‘sakkāyadiṭṭhi
Stress is on : both sakkāya and sakkāyadiṭṭhi
(same as VisuddhiMagga Atthakatha)
3.Abhidhamma-Vibhanga Atthakatha
Paṭiccasamuppādavibhaṅgo
Suttantabhājanīyaṃ
Upādānapadaniddeso
Line of interest :Vīsativatthukā sakkāyadiṭṭhi attavādupādānaṃ.
Yathāha – ‘‘tattha katamaṃ attavādupādānaṃ? Idha assutavā puthujjano…pe… sappurisadhamme avinīto rūpaṃ attato samanupassati…pe… vipariyesaggāho
Stress is on : List of views (20) sakkāyadiṭṭhi represents and its relation to 4th upadana
extended version of that pe(peyyalam) can be found in
Abhidhamma-Dhammasangani
nikkhepakaṇḍaṃ
tikanikkhepaṃ
4.I understand you asked only for commentaries ,but the same information can be found in
MN 44, MN 109
KN-Netti-nayasamuṭṭhānaṃ
Good luck.