I've just recently reached the same point. Feels weird, doesn't it?
Although your DH was IIIA, my understanding is that a IIIA with chemo has less recurrence risk than many stage IIs. So there's nothing in your profile that shouts that more follow-up is needed or justified.
Although I've been discharged, my doctor did emphasise that if I have any symptoms, to come straight back. Hopefully yours is the same. Good luck.
EDIT: I'm on a 5 year cycle for colonoscopies now.
31 year old male, dx Oct 17
Staged IIA post sigmoid colectomy
T3b N0 M0
LVI-, PNI-, MSS
Oct 18: clear CT
Oct 19: clear CT
Nov 19: became a father!
Oct 20: clear CT
Nov 20: clear colonoscopy
Nov 21: no more CTs but still being monitored and NED
Aug 22: clear MRI (tailbone pain triggers a scan)
Nov 22: 5 years cancer-free, discharged from follow-ups
CEA: always 1