As a couple, what bank accounts will give a high i/r for our combined monthly savings or even investment instruments we can put our money in?

You can try going with high interest bank accounts for a start. Eg there is a dbs multiplier account "hack" that you can both try.

Simply open a joint dbs account as a couple and inform your hrs to credit both your salaries into this joint account. You and your partner will also need to individually set up a new dbs multiplier account each.

Both your salaries will then be recognized as valid transactions to help reach the higher interest rate tier.

Then both of you can concentrate your credit card spending eg on groceries on posb everyday card etc. These transactions will also add on to your valid transactions for the month, again to help push you up to the higher tier.

Do an internal transfer of your salary from the joint account to your individual multiplier accounts as the higher interests are calculated on the average monthly total inside your individual multiplier account. Top up to 50k per person if you can. If you have more than that and up to 100k, you will need to achieve more transaction categories like buying dbs insurance, getting dbs home loans or have investment transaction with dbs.

You and your partner can also apply for a regular savings plan (rsp) on dbs/posb eg on ABF Singapore Bond Index Fund or Nikko AM Singapore STI ETF, setting aside a small amount of at least $100, monthly. First 12 months this will be counted as valid investment transactions. You and your partner can use the $200 each for this DBS invest-saver program as a passive long term investment plan.

If course if you have a house and using dbs for your home loans and insurance, you will be able to unlock the additional transaction tiers as well.

If you both can contribute $50 more each month, then with a joint bank account, joint CDP account, you can both have Singapore savings bonds with $500 lowest entry.

Else, perhaps you can find a high interest bank account such as CIMB or UOB One which does not have salary requirement.