Assuming you have healed uneventfully, all your skin incisions and the muscle repairs have healed adequately and strongly. Scar tissue is not yet mature, softened, and faded maximally--that will take 6-12 months. As long as your scars are pink, they should NOT be exposed to ultraviolet of any type (sun or tanning bed) or else your scars can turn dark and will remain permanently so.
Also, your sensation has not returned completely, so you do NOT have the normal protective response to too-hot temperatures, and could burn and blister breast or abdominal skin that is still numb. I'd consider avoiding the super-hot sauna or steam room for now, just to be on the safe side.
But, your abdominal muscle repair is durable, so as long as you are not kickboxing or doing full-contact tackle football at your spa event, you should be fine, even for starting to work out gradually.
Otherwise, you should check with your surgeon, who has your best interests at heart, not on-line consultants who have not seen or monitored your progress. Enjoy your well-deserved spa day!