Considering your usage and budget, you can look at bikes like the Royal Enfield Hunter / Bullet / Classic 350, Honda CB350 trio, TVS Ronin and the Hero Xpulse 210. All have spacious seats, comfortable suspension and have decent braking performance too. A test ride of all these machines with your wife sitting behind you will help you decide which is the right fit for you. 

Do bear in mind that making the switch from a scooter to a motorcycle will need good hand and foot coordination to operate the clutch and gear pedal.  We recommend you practice on a used bike first before taking the plunge. 

If you want to stay in the same displacement range as your Unicorn, you can look at the Bajaj Pulsar N160 and the TVS Apache RTR 160 4V. Both have great suspension, peppy performance and will return similar fuel economy to your Unicorn. 

If you want to make a step up, then bikes like the Royal Enfield Hunter / Bullet / Classic 350, TVS Ronin, and Honda CB350 trio will make for good commuting partners. These are bikes with upright, neutral ergonomics, plush suspension setups and torquey, smooth engines. Expect lower fuel economy in comparison to your Unicorn, however, by virtue of its larger displacement.

Lastly, the Hero Xpulse 210 is a wonderful do-it-all machine which will have the best suspension comfort of all the bikes listed here.

A test ride of all of these bikes will help you determine which one is best for you.

Since you have mentioned you want a retro bike and are looking in the 350cc category, you could take a look at the Royal Enfield Bullet 350. It has the same engine as your brother's Hunter. It will offer you a more spacious riding position and a laid-back riding experience, not to mention more road presence, if that is something that matters to you. 

Writing the Yamaha XSR155 off because its engine is "just 155cc" would be a mistake in our opinion. Because its performance belies its displacement, and it will give you great fuel efficiency and also last you a long time. 

Take a test ride of these two to see which one suits you better.  

All three of the Royal Enfield 350s you have shortlisted will serve you well, but each has a different character. The Hunter 350 is the lightest and most affordable one and will be the most agile in the city, where you spend most of your time. The Bullet is a retro roadster with a commanding riding position that is going to feel quite a big larger. This will be the most comfortable bike owing to its neutral ergonomics and great suspension. The Meteor 350, with its laid-back rider triangle, will feel the most relaxed to sit on. But all your weight will be on your tailbone, which won't be ideal when tackling road imperfections. 

Of the three, the Hunter makes the most sense for your usage, but a test ride of all three will help clear the picture for you. 

Since you have had a good experience with your Honda Hornet, you could stick with the same brand and step up to any of the Honda CB350 models. All are mechanically very similar, and picking between the three comes down largely to which one you prefer the look of, as well as pricing. All three are comfortable, torquey, well-finished and decently fuel-efficient machines. 

If you want to switch things up, Royal Enfield has three 350cc machines which deserve your attention - Hunter, Bullet and Classic. The Hunter is the lightest and most agile machine of these three and will feel the smallest, too. 

The Bullet and Classic are considerably heavier and have commanding riding positions and great suspension. 

A test ride of all these 350s should help you decide which is the best option for you. 

The Royal Enfield Hunter 350 is the lightest machine in the company's portfolio and will feel quite at home in the city and at the highway speeds you ride at. The Royal Enfield Bullet 350 is a neo-retro roadster that will have the most comfort owing to its spacious, upright ergonomics and lovely ride quality. 

The Meteor 350 will have the most laid-back seating position, but over bad roads, a lot of road imperfections will filter through to your spine. 

A test ride of all three should help you decide which is best for you.