Bulgaria Trip - Advice On One Daytrip

I will be in Bulgaria for 8 days this summer and have almost all of my itinerary planned out, I am just stuck on one potential day trip. I do love history, outdoors, and culture. I will be using Sofia as a base.

Day 1 and Day 2 :Sofia

Day 3: Booked day tour to Skopje

Day 4: Sofia - spa and massage day and relaxing

Day 5 Early train for solo daytrip to Plovdiv

Day 6: Sofia museums

Day 7: Unknown

Day 8: Wind down in Sofia, relax, pool, spa, last minute tourist attractions.

For day 7, please help me decide between the following tour daytrip:

1. Rila Monastery and Melnik combined

2. Rila Monastery and Boyana

3. Belogradchik Rocks & Belogradchik Fortress

Full Day Tour

Thank you for any suggestions!